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 $57.63   7.523%   $61.9655   $61.97   $61.95   $62.00  
  Purchase #2 $47.50   12.719%   $53.5415   $53.54   $53.55   $53.50  
  Purchase #3 $248.65   12.820%   $280.5269   $280.53   $280.55   $280.50  
  Purchase #4 $213.67   6.781%   $228.159   $228.16   $228.15   $228.20  
  Purchase #5 $6.71   13.469%   $7.6138   $7.61   $7.60   $7.60  
  Purchase #6 $148.27   12.760%   $167.1893   $167.19   $167.20   $167.20  
  Purchase #7 $17.79   5.289%   $18.7309   $18.73   $18.75   $18.70  
  7 purchase totals = $740.22       $817.7269   $817.73   $817.75   $817.70