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 $44.32   4.830%   $46.4607   $46.46   $46.45   $46.50  
  Purchase #2 $138.91   8.237%   $150.352   $150.35   $150.35   $150.40  
  Purchase #3 $230.56   7.268%   $247.3171   $247.32   $247.30   $247.30  
  Purchase #4 $25.68   10.389%   $28.3479   $28.35   $28.35   $28.30  
  Purchase #5 $13.40   13.623%   $15.2255   $15.23   $15.25   $15.20  
  Purchase #6 $217.51   3.153%   $224.3681   $224.37   $224.35   $224.40  
  Purchase #7 $210.90   13.718%   $239.8313   $239.83   $239.85   $239.80  
  7 purchase totals = $881.28       $951.9026   $951.91   $951.90   $951.90