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 $194.66   5.120%   $204.6266   $204.63   $204.65   $204.60  
  Purchase #2 $91.80   6.161%   $97.4558   $97.46   $97.45   $97.50  
  Purchase #3 $188.29   5.446%   $198.5443   $198.54   $198.55   $198.50  
  Purchase #4 $223.76   7.389%   $240.2936   $240.29   $240.30   $240.30  
  Purchase #5 $64.43   12.787%   $72.6687   $72.67   $72.65   $72.70  
  Purchase #6 $20.30   4.710%   $21.2561   $21.26   $21.25   $21.30  
  Purchase #7 $172.83   9.640%   $189.4908   $189.49   $189.50   $189.50  
  7 purchase totals = $956.07       $1,024.3359   $1,024.34   $1,024.35   $1,024.40