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 $68.97   7.738%   $74.3069   $74.31   $74.30   $74.30  
  Purchase #2 $243.26   6.626%   $259.3784   $259.38   $259.40   $259.40  
  Purchase #3 $165.83   9.447%   $181.496   $181.50   $181.50   $181.50  
  Purchase #4 $209.51   12.346%   $235.3761   $235.38   $235.40   $235.40  
  Purchase #5 $71.37   7.176%   $76.4915   $76.49   $76.50   $76.50  
  Purchase #6 $26.73   10.369%   $29.5016   $29.50   $29.50   $29.50  
  Purchase #7 $95.48   6.347%   $101.5401   $101.54   $101.55   $101.50  
  7 purchase totals = $881.15       $958.0906   $958.10   $958.15   $958.10