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 $235.50   12.632%   $265.2484   $265.25   $265.25   $265.20  
  Purchase #2 $111.85   9.789%   $122.799   $122.80   $122.80   $122.80  
  Purchase #3 $9.54   10.575%   $10.5489   $10.55   $10.55   $10.50  
  Purchase #4 $54.34   8.502%   $58.96   $58.96   $58.95   $59.00  
  Purchase #5 $12.85   3.477%   $13.2968   $13.30   $13.30   $13.30  
  Purchase #6 $96.84   6.348%   $102.9874   $102.99   $103.00   $103.00  
  Purchase #7 $229.99   6.566%   $245.0911   $245.09   $245.10   $245.10  
  7 purchase totals = $750.91       $818.9316   $818.94   $818.95   $818.90