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 $212.79   11.260%   $236.7502   $236.75   $236.75   $236.80  
  Purchase #2 $183.26   6.544%   $195.2525   $195.25   $195.25   $195.30  
  Purchase #3 $243.72   7.482%   $261.9551   $261.96   $261.95   $262.00  
  Purchase #4 $225.84   4.401%   $235.7792   $235.78   $235.80   $235.80  
  Purchase #5 $10.89   4.561%   $11.3867   $11.39   $11.40   $11.40  
  Purchase #6 $192.44   10.533%   $212.7097   $212.71   $212.70   $212.70  
  Purchase #7 $172.55   5.790%   $182.5406   $182.54   $182.55   $182.50  
  7 purchase totals = $1,241.49       $1,336.3740   $1,336.38   $1,336.40   $1,336.50