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 $234.98   13.609%   $266.9584   $266.96   $266.95   $267.00  
  Purchase #2 $139.92   9.508%   $153.2236   $153.22   $153.20   $153.20  
  Purchase #3 $157.26   3.570%   $162.8742   $162.87   $162.85   $162.90  
  Purchase #4 $143.49   12.511%   $161.442   $161.44   $161.45   $161.40  
  Purchase #5 $236.32   13.193%   $267.4977   $267.50   $267.50   $267.50  
  Purchase #6 $74.31   12.782%   $83.8083   $83.81   $83.80   $83.80  
  Purchase #7 $177.74   12.159%   $199.3514   $199.35   $199.35   $199.40  
  7 purchase totals = $1,164.02       $1,295.1556   $1,295.15   $1,295.10   $1,295.20