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 $41.39   3.798%   $42.962   $42.96   $42.95   $43.00  
  Purchase #2 $82.48   12.123%   $92.4791   $92.48   $92.50   $92.50  
  Purchase #3 $137.50   11.309%   $153.0499   $153.05   $153.05   $153.00  
  Purchase #4 $67.33   10.132%   $74.1519   $74.15   $74.15   $74.20  
  Purchase #5 $170.78   8.185%   $184.7583   $184.76   $184.75   $184.80  
  Purchase #6 $217.96   10.540%   $240.933   $240.93   $240.95   $240.90  
  Purchase #7 $114.43   4.824%   $119.9501   $119.95   $119.95   $120.00  
  7 purchase totals = $831.87       $908.2843   $908.28   $908.30   $908.40