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 $63.44   6.769%   $67.7343   $67.73   $67.75   $67.70  
  Purchase #2 $80.76   13.576%   $91.724   $91.72   $91.70   $91.70  
  Purchase #3 $217.95   12.515%   $245.2264   $245.23   $245.25   $245.20  
  Purchase #4 $125.50   8.706%   $136.426   $136.43   $136.45   $136.40  
  Purchase #5 $91.91   11.760%   $102.7186   $102.72   $102.70   $102.70  
  Purchase #6 $34.75   11.284%   $38.6712   $38.67   $38.65   $38.70  
  Purchase #7 $209.48   11.871%   $234.3474   $234.35   $234.35   $234.30  
  7 purchase totals = $823.79       $916.8479   $916.85   $916.85   $916.70