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 $84.42   13.347%   $95.6875   $95.69   $95.70   $95.70  
  Purchase #2 $110.75   12.112%   $124.164   $124.16   $124.15   $124.20  
  Purchase #3 $174.87   7.243%   $187.5358   $187.54   $187.55   $187.50  
  Purchase #4 $31.95   13.828%   $36.368   $36.37   $36.35   $36.40  
  Purchase #5 $138.35   10.787%   $153.2738   $153.27   $153.25   $153.30  
  Purchase #6 $190.39   5.563%   $200.9814   $200.98   $201.00   $201.00  
  Purchase #7 $16.95   9.836%   $18.6172   $18.62   $18.60   $18.60  
  7 purchase totals = $747.68       $816.6277   $816.63   $816.60   $816.70