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 $240.47   11.591%   $268.3429   $268.34   $268.35   $268.30  
  Purchase #2 $49.49   10.133%   $54.5048   $54.50   $54.50   $54.50  
  Purchase #3 $226.31   13.390%   $256.6129   $256.61   $256.60   $256.60  
  Purchase #4 $210.81   11.494%   $235.0405   $235.04   $235.05   $235.00  
  Purchase #5 $141.62   12.540%   $159.3791   $159.38   $159.40   $159.40  
  Purchase #6 $150.99   11.262%   $167.9945   $167.99   $168.00   $168.00  
  Purchase #7 $182.27   9.134%   $198.9185   $198.92   $198.90   $198.90  
  7 purchase totals = $1,201.96       $1,340.7932   $1,340.78   $1,340.80   $1,340.70