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 $61.71   10.213%   $68.0124   $68.01   $68.00   $68.00  
  Purchase #2 $167.97   6.334%   $178.6092   $178.61   $178.60   $178.60  
  Purchase #3 $75.33   11.367%   $83.8928   $83.89   $83.90   $83.90  
  Purchase #4 $215.46   13.375%   $244.2778   $244.28   $244.30   $244.30  
  Purchase #5 $195.44   11.706%   $218.3182   $218.32   $218.30   $218.30  
  Purchase #6 $37.41   10.526%   $41.3478   $41.35   $41.35   $41.30  
  Purchase #7 $90.97   6.667%   $97.035   $97.04   $97.05   $97.00  
  7 purchase totals = $844.29       $931.4932   $931.50   $931.50   $931.40