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 $69.74   11.470%   $77.7392   $77.74   $77.75   $77.70  
  Purchase #2 $169.98   7.447%   $182.6384   $182.64   $182.65   $182.60  
  Purchase #3 $215.28   13.755%   $244.8918   $244.89   $244.90   $244.90  
  Purchase #4 $234.33   11.581%   $261.4678   $261.47   $261.45   $261.50  
  Purchase #5 $223.93   10.523%   $247.4942   $247.49   $247.50   $247.50  
  Purchase #6 $46.95   6.838%   $50.1604   $50.16   $50.15   $50.20  
  Purchase #7 $172.71   8.571%   $187.513   $187.51   $187.50   $187.50  
  7 purchase totals = $1,132.92       $1,251.9048   $1,251.90   $1,251.90   $1,251.90