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 $84.99   9.737%   $93.2655   $93.27   $93.25   $93.30  
  Purchase #2 $96.45   8.298%   $104.4534   $104.45   $104.45   $104.50  
  Purchase #3 $123.87   11.441%   $138.042   $138.04   $138.05   $138.00  
  Purchase #4 $215.35   4.370%   $224.7608   $224.76   $224.75   $224.80  
  Purchase #5 $48.50   8.682%   $52.7108   $52.71   $52.70   $52.70  
  Purchase #6 $198.65   6.248%   $211.0617   $211.06   $211.05   $211.10  
  Purchase #7 $125.52   4.526%   $131.201   $131.20   $131.20   $131.20  
  7 purchase totals = $893.33       $955.4952   $955.49   $955.45   $955.60