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 $63.60   11.504%   $70.9165   $70.92   $70.90   $70.90  
  Purchase #2 $233.44   5.795%   $246.9678   $246.97   $246.95   $247.00  
  Purchase #3 $58.34   4.582%   $61.0131   $61.01   $61.00   $61.00  
  Purchase #4 $98.66   5.621%   $104.2057   $104.21   $104.20   $104.20  
  Purchase #5 $33.55   4.503%   $35.0608   $35.06   $35.05   $35.10  
  Purchase #6 $249.28   8.592%   $270.6981   $270.70   $270.70   $270.70  
  Purchase #7 $87.56   5.465%   $92.3452   $92.35   $92.35   $92.30  
  7 purchase totals = $824.43       $881.2072   $881.22   $881.15   $881.20