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 $208.25   12.258%   $233.7773   $233.78   $233.80   $233.80  
  Purchase #2 $41.96   6.107%   $44.5225   $44.52   $44.50   $44.50  
  Purchase #3 $185.25   13.871%   $210.946   $210.95   $210.95   $210.90  
  Purchase #4 $58.76   6.207%   $62.4072   $62.41   $62.40   $62.40  
  Purchase #5 $119.34   12.173%   $133.8673   $133.87   $133.85   $133.90  
  Purchase #6 $182.75   13.537%   $207.4889   $207.49   $207.50   $207.50  
  Purchase #7 $28.87   13.224%   $32.6878   $32.69   $32.70   $32.70  
  7 purchase totals = $825.18       $925.6970   $925.71   $925.70   $925.70