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 $54.34   8.797%   $59.1203   $59.12   $59.10   $59.10  
  Purchase #2 $114.28   10.376%   $126.1377   $126.14   $126.15   $126.10  
  Purchase #3 $215.54   11.795%   $240.9629   $240.96   $240.95   $241.00  
  Purchase #4 $88.59   5.862%   $93.7831   $93.78   $93.80   $93.80  
  Purchase #5 $228.49   9.102%   $249.2872   $249.29   $249.30   $249.30  
  Purchase #6 $245.95   5.814%   $260.2495   $260.25   $260.25   $260.20  
  Purchase #7 $107.45   11.293%   $119.5843   $119.58   $119.60   $119.60  
  7 purchase totals = $1,054.64       $1,149.1250   $1,149.12   $1,149.15   $1,149.10