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 $213.65   10.471%   $236.0213   $236.02   $236.00   $236.00  
  Purchase #2 $73.41   10.794%   $81.3339   $81.33   $81.35   $81.30  
  Purchase #3 $195.47   7.830%   $210.7753   $210.78   $210.80   $210.80  
  Purchase #4 $97.67   3.209%   $100.8042   $100.80   $100.80   $100.80  
  Purchase #5 $54.84   9.387%   $59.9878   $59.99   $60.00   $60.00  
  Purchase #6 $52.88   8.541%   $57.3965   $57.40   $57.40   $57.40  
  Purchase #7 $246.34   11.804%   $275.418   $275.42   $275.40   $275.40  
  7 purchase totals = $934.26       $1,021.7370   $1,021.74   $1,021.75   $1,021.70