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 $154.61   9.474%   $169.2578   $169.26   $169.25   $169.30  
  Purchase #2 $121.76   8.778%   $132.4481   $132.45   $132.45   $132.40  
  Purchase #3 $183.31   4.198%   $191.0054   $191.01   $191.00   $191.00  
  Purchase #4 $147.42   9.541%   $161.4853   $161.49   $161.50   $161.50  
  Purchase #5 $109.64   4.406%   $114.4707   $114.47   $114.45   $114.50  
  Purchase #6 $163.26   10.385%   $180.2146   $180.21   $180.20   $180.20  
  Purchase #7 $46.27   7.358%   $49.6745   $49.67   $49.65   $49.70  
  7 purchase totals = $926.27       $998.5564   $998.56   $998.50   $998.60