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 $122.39   9.743%   $134.3145   $134.31   $134.30   $134.30  
  Purchase #2 $44.76   4.679%   $46.8543   $46.85   $46.85   $46.90  
  Purchase #3 $184.56   13.559%   $209.5845   $209.58   $209.60   $209.60  
  Purchase #4 $179.54   6.661%   $191.4992   $191.50   $191.50   $191.50  
  Purchase #5 $132.50   10.211%   $146.0296   $146.03   $146.05   $146.00  
  Purchase #6 $23.63   5.567%   $24.9455   $24.95   $24.95   $24.90  
  Purchase #7 $60.72   8.356%   $65.7938   $65.79   $65.80   $65.80  
  7 purchase totals = $748.10       $819.0214   $819.01   $819.05   $819.00