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 $86.34   7.209%   $92.5643   $92.56   $92.55   $92.60  
  Purchase #2 $146.37   3.417%   $151.3715   $151.37   $151.35   $151.40  
  Purchase #3 $171.28   4.873%   $179.6265   $179.63   $179.65   $179.60  
  Purchase #4 $54.99   5.678%   $58.1123   $58.11   $58.10   $58.10  
  Purchase #5 $34.97   10.411%   $38.6107   $38.61   $38.60   $38.60  
  Purchase #6 $219.51   11.517%   $244.791   $244.79   $244.80   $244.80  
  Purchase #7 $115.88   4.677%   $121.2997   $121.30   $121.30   $121.30  
  7 purchase totals = $829.34       $886.3760   $886.37   $886.35   $886.40