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 $241.65   10.605%   $267.277   $267.28   $267.30   $267.30  
  Purchase #2 $44.98   13.778%   $51.1773   $51.18   $51.20   $51.20  
  Purchase #3 $134.74   13.553%   $153.0013   $153.00   $153.00   $153.00  
  Purchase #4 $59.74   10.414%   $65.9613   $65.96   $65.95   $66.00  
  Purchase #5 $185.48   7.141%   $198.7251   $198.73   $198.75   $198.70  
  Purchase #6 $60.46   12.828%   $68.2158   $68.22   $68.20   $68.20  
  Purchase #7 $93.40   8.333%   $101.183   $101.18   $101.20   $101.20  
  7 purchase totals = $820.45       $905.5408   $905.55   $905.60   $905.60