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 $113.93   3.186%   $117.5598   $117.56   $117.55   $117.60  
  Purchase #2 $60.31   12.753%   $68.0013   $68.00   $68.00   $68.00  
  Purchase #3 $14.86   4.707%   $15.5595   $15.56   $15.55   $15.60  
  Purchase #4 $248.43   4.868%   $260.5236   $260.52   $260.50   $260.50  
  Purchase #5 $227.64   9.620%   $249.539   $249.54   $249.55   $249.50  
  Purchase #6 $138.98   5.292%   $146.3348   $146.33   $146.35   $146.30  
  Purchase #7 $140.87   10.544%   $155.7233   $155.72   $155.70   $155.70  
  7 purchase totals = $945.02       $1,013.2413   $1,013.23   $1,013.20   $1,013.20