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 $29.75   5.686%   $31.4416   $31.44   $31.45   $31.40  
  Purchase #2 $209.71   10.640%   $232.0231   $232.02   $232.00   $232.00  
  Purchase #3 $22.83   11.810%   $25.5262   $25.53   $25.55   $25.50  
  Purchase #4 $20.66   10.411%   $22.8109   $22.81   $22.80   $22.80  
  Purchase #5 $64.25   7.741%   $69.2236   $69.22   $69.20   $69.20  
  Purchase #6 $17.64   8.428%   $19.1267   $19.13   $19.15   $19.10  
  Purchase #7 $112.45   4.383%   $117.3787   $117.38   $117.40   $117.40  
  7 purchase totals = $477.29       $517.5308   $517.53   $517.55   $517.40