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 $194.61   6.228%   $206.7303   $206.73   $206.75   $206.70  
  Purchase #2 $185.53   9.328%   $202.8362   $202.84   $202.85   $202.80  
  Purchase #3 $25.50   7.374%   $27.3804   $27.38   $27.40   $27.40  
  Purchase #4 $70.99   11.118%   $78.8827   $78.88   $78.90   $78.90  
  Purchase #5 $44.83   7.311%   $48.1075   $48.11   $48.10   $48.10  
  Purchase #6 $54.51   7.491%   $58.5933   $58.59   $58.60   $58.60  
  Purchase #7 $11.88   6.117%   $12.6067   $12.61   $12.60   $12.60  
  7 purchase totals = $587.85       $635.1371   $635.14   $635.20   $635.10