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 $93.86   4.693%   $98.2648   $98.26   $98.25   $98.30  
  Purchase #2 $145.33   8.259%   $157.3328   $157.33   $157.35   $157.30  
  Purchase #3 $189.67   13.619%   $215.5012   $215.50   $215.50   $215.50  
  Purchase #4 $151.38   6.753%   $161.6027   $161.60   $161.60   $161.60  
  Purchase #5 $20.43   13.708%   $23.2305   $23.23   $23.25   $23.20  
  Purchase #6 $227.88   12.787%   $257.019   $257.02   $257.00   $257.00  
  Purchase #7 $98.49   10.220%   $108.5557   $108.56   $108.55   $108.60  
  7 purchase totals = $927.04       $1,021.5067   $1,021.50   $1,021.50   $1,021.50