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 $243.33   9.604%   $266.6994   $266.70   $266.70   $266.70  
  Purchase #2 $138.99   6.734%   $148.3496   $148.35   $148.35   $148.30  
  Purchase #3 $204.63   6.386%   $217.6977   $217.70   $217.70   $217.70  
  Purchase #4 $162.40   13.783%   $184.7836   $184.78   $184.80   $184.80  
  Purchase #5 $63.75   7.509%   $68.537   $68.54   $68.55   $68.50  
  Purchase #6 $23.28   8.145%   $25.1762   $25.18   $25.20   $25.20  
  Purchase #7 $127.64   4.577%   $133.4821   $133.48   $133.50   $133.50  
  7 purchase totals = $964.02       $1,044.7256   $1,044.73   $1,044.80   $1,044.70