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 $152.43   8.103%   $164.7814   $164.78   $164.80   $164.80  
  Purchase #2 $119.69   5.399%   $126.1521   $126.15   $126.15   $126.20  
  Purchase #3 $29.54   5.529%   $31.1733   $31.17   $31.15   $31.20  
  Purchase #4 $228.42   11.347%   $254.3388   $254.34   $254.35   $254.30  
  Purchase #5 $154.32   12.494%   $173.6007   $173.60   $173.60   $173.60  
  Purchase #6 $128.42   5.284%   $135.2057   $135.21   $135.20   $135.20  
  Purchase #7 $138.62   9.662%   $152.0135   $152.01   $152.00   $152.00  
  7 purchase totals = $951.44       $1,037.2655   $1,037.26   $1,037.25   $1,037.30