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 $63.58   5.228%   $66.904   $66.90   $66.90   $66.90  
  Purchase #2 $73.43   13.573%   $83.3967   $83.40   $83.40   $83.40  
  Purchase #3 $66.48   13.803%   $75.6562   $75.66   $75.65   $75.70  
  Purchase #4 $201.95   6.587%   $215.2524   $215.25   $215.25   $215.30  
  Purchase #5 $5.88   4.685%   $6.1555   $6.16   $6.15   $6.20  
  Purchase #6 $120.29   9.497%   $131.7139   $131.71   $131.70   $131.70  
  Purchase #7 $202.82   6.249%   $215.4942   $215.49   $215.50   $215.50  
  7 purchase totals = $734.43       $794.5729   $794.57   $794.55   $794.70