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 $152.25   13.873%   $173.3716   $173.37   $173.35   $173.40  
  Purchase #2 $29.26   10.815%   $32.4245   $32.42   $32.40   $32.40  
  Purchase #3 $109.26   6.426%   $116.281   $116.28   $116.30   $116.30  
  Purchase #4 $66.47   5.681%   $70.2462   $70.25   $70.25   $70.20  
  Purchase #5 $236.66   4.255%   $246.7299   $246.73   $246.75   $246.70  
  Purchase #6 $191.73   8.740%   $208.4872   $208.49   $208.50   $208.50  
  Purchase #7 $164.74   7.610%   $177.2767   $177.28   $177.30   $177.30  
  7 purchase totals = $950.37       $1,024.8171   $1,024.82   $1,024.85   $1,024.80