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 $102.65   13.580%   $116.5899   $116.59   $116.60   $116.60  
  Purchase #2 $138.58   9.848%   $152.2274   $152.23   $152.25   $152.20  
  Purchase #3 $61.38   3.597%   $63.5878   $63.59   $63.60   $63.60  
  Purchase #4 $125.61   8.443%   $136.2153   $136.22   $136.20   $136.20  
  Purchase #5 $184.94   4.799%   $193.8153   $193.82   $193.80   $193.80  
  Purchase #6 $70.83   5.293%   $74.579   $74.58   $74.60   $74.60  
  Purchase #7 $199.88   13.673%   $227.2096   $227.21   $227.20   $227.20  
  7 purchase totals = $883.87       $964.2243   $964.24   $964.25   $964.20