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 $246.84   8.391%   $267.5523   $267.55   $267.55   $267.60  
  Purchase #2 $127.26   6.578%   $135.6312   $135.63   $135.65   $135.60  
  Purchase #3 $51.86   5.412%   $54.6667   $54.67   $54.65   $54.70  
  Purchase #4 $70.47   7.467%   $75.732   $75.73   $75.75   $75.70  
  Purchase #5 $14.91   8.323%   $16.151   $16.15   $16.15   $16.20  
  Purchase #6 $163.50   3.475%   $169.1816   $169.18   $169.20   $169.20  
  Purchase #7 $22.80   10.754%   $25.2519   $25.25   $25.25   $25.30  
  7 purchase totals = $697.64       $744.1667   $744.16   $744.20   $744.30