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 $239.33   11.766%   $267.4896   $267.49   $267.50   $267.50  
  Purchase #2 $165.42   8.337%   $179.2111   $179.21   $179.20   $179.20  
  Purchase #3 $125.84   8.511%   $136.5502   $136.55   $136.55   $136.60  
  Purchase #4 $119.35   4.731%   $124.9964   $125.00   $125.00   $125.00  
  Purchase #5 $118.63   6.755%   $126.6435   $126.64   $126.65   $126.60  
  Purchase #6 $71.86   9.170%   $78.4496   $78.45   $78.45   $78.40  
  Purchase #7 $93.48   3.827%   $97.0575   $97.06   $97.05   $97.10  
  7 purchase totals = $933.91       $1,010.3979   $1,010.40   $1,010.40   $1,010.40