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 $114.35   11.288%   $127.2578   $127.26   $127.25   $127.30  
  Purchase #2 $151.74   11.872%   $169.7546   $169.75   $169.75   $169.80  
  Purchase #3 $67.63   12.428%   $76.0351   $76.04   $76.05   $76.00  
  Purchase #4 $246.46   8.733%   $267.9834   $267.98   $268.00   $268.00  
  Purchase #5 $207.81   11.681%   $232.0843   $232.08   $232.10   $232.10  
  Purchase #6 $77.86   9.543%   $85.2902   $85.29   $85.30   $85.30  
  Purchase #7 $113.87   11.404%   $126.8557   $126.86   $126.85   $126.90  
  7 purchase totals = $979.72       $1,085.2611   $1,085.26   $1,085.30   $1,085.40