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 $64.56   3.672%   $66.9306   $66.93   $66.95   $66.90  
  Purchase #2 $6.46   11.446%   $7.1994   $7.20   $7.20   $7.20  
  Purchase #3 $210.27   12.194%   $235.9103   $235.91   $235.90   $235.90  
  Purchase #4 $97.56   4.237%   $101.6936   $101.69   $101.70   $101.70  
  Purchase #5 $249.64   4.293%   $260.357   $260.36   $260.35   $260.40  
  Purchase #6 $14.72   6.589%   $15.6899   $15.69   $15.70   $15.70  
  Purchase #7 $206.56   10.253%   $227.7386   $227.74   $227.75   $227.70  
  7 purchase totals = $849.77       $915.5194   $915.52   $915.55   $915.50