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 $152.86   11.799%   $170.896   $170.90   $170.90   $170.90  
  Purchase #2 $213.34   9.384%   $233.3598   $233.36   $233.35   $233.40  
  Purchase #3 $250.51   12.583%   $282.0317   $282.03   $282.05   $282.00  
  Purchase #4 $196.67   11.311%   $218.9153   $218.92   $218.90   $218.90  
  Purchase #5 $64.67   5.729%   $68.3749   $68.37   $68.35   $68.40  
  Purchase #6 $156.51   9.762%   $171.7885   $171.79   $171.80   $171.80  
  Purchase #7 $236.99   11.809%   $264.9761   $264.98   $265.00   $265.00  
  7 purchase totals = $1,271.55       $1,410.3423   $1,410.35   $1,410.35   $1,410.40