Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $219.27   9.569%   $240.2519   $240.25   $240.25   $240.30  
  Purchase #2 $203.68   11.170%   $226.4311   $226.43   $226.45   $226.40  
  Purchase #3 $131.32   7.691%   $141.4198   $141.42   $141.40   $141.40  
  Purchase #4 $247.71   12.190%   $277.9058   $277.91   $277.90   $277.90  
  Purchase #5 $213.59   10.761%   $236.5744   $236.57   $236.55   $236.60  
  Purchase #6 $206.95   4.452%   $216.1634   $216.16   $216.15   $216.20  
  Purchase #7 $117.80   12.364%   $132.3648   $132.36   $132.35   $132.40  
  7 purchase totals = $1,340.32       $1,471.1112   $1,471.10   $1,471.05   $1,471.20