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 $245.66   6.230%   $260.9646   $260.96   $260.95   $261.00  
  Purchase #2 $146.40   4.548%   $153.0583   $153.06   $153.05   $153.10  
  Purchase #3 $39.67   6.595%   $42.2862   $42.29   $42.30   $42.30  
  Purchase #4 $18.30   6.699%   $19.5259   $19.53   $19.55   $19.50  
  Purchase #5 $224.28   9.633%   $245.8849   $245.88   $245.90   $245.90  
  Purchase #6 $167.62   6.188%   $177.9923   $177.99   $178.00   $178.00  
  Purchase #7 $92.94   3.196%   $95.9104   $95.91   $95.90   $95.90  
  7 purchase totals = $934.87       $995.6226   $995.62   $995.65   $995.70