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 $60.39   6.236%   $64.1559   $64.16   $64.15   $64.20  
  Purchase #2 $249.48   10.172%   $274.8571   $274.86   $274.85   $274.90  
  Purchase #3 $166.77   7.111%   $178.629   $178.63   $178.65   $178.60  
  Purchase #4 $85.85   7.472%   $92.2647   $92.26   $92.25   $92.30  
  Purchase #5 $205.68   11.146%   $228.6051   $228.61   $228.60   $228.60  
  Purchase #6 $166.33   8.631%   $180.6859   $180.69   $180.70   $180.70  
  Purchase #7 $16.85   12.307%   $18.9237   $18.92   $18.90   $18.90  
  7 purchase totals = $951.35       $1,038.1214   $1,038.13   $1,038.10   $1,038.20