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 $62.67   9.557%   $68.6594   $68.66   $68.65   $68.70  
  Purchase #2 $104.47   7.776%   $112.5936   $112.59   $112.60   $112.60  
  Purchase #3 $110.83   8.586%   $120.3459   $120.35   $120.35   $120.30  
  Purchase #4 $224.93   9.758%   $246.8787   $246.88   $246.90   $246.90  
  Purchase #5 $205.40   8.266%   $222.3784   $222.38   $222.40   $222.40  
  Purchase #6 $199.42   7.345%   $214.0674   $214.07   $214.05   $214.10  
  Purchase #7 $16.34   7.360%   $17.5426   $17.54   $17.55   $17.50  
  7 purchase totals = $924.06       $1,002.4660   $1,002.47   $1,002.50   $1,002.50