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 $234.45   11.175%   $260.6498   $260.65   $260.65   $260.60  
  Purchase #2 $89.90   12.359%   $101.0107   $101.01   $101.00   $101.00  
  Purchase #3 $244.29   4.555%   $255.4174   $255.42   $255.40   $255.40  
  Purchase #4 $35.44   12.117%   $39.7343   $39.73   $39.75   $39.70  
  Purchase #5 $173.52   10.429%   $191.6164   $191.62   $191.60   $191.60  
  Purchase #6 $141.85   5.490%   $149.6376   $149.64   $149.65   $149.60  
  Purchase #7 $191.94   7.374%   $206.0937   $206.09   $206.10   $206.10  
  7 purchase totals = $1,111.39       $1,204.1599   $1,204.16   $1,204.15   $1,204.00