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 $216.51   12.827%   $244.2817   $244.28   $244.30   $244.30  
  Purchase #2 $249.38   11.232%   $277.3904   $277.39   $277.40   $277.40  
  Purchase #3 $14.95   6.234%   $15.882   $15.88   $15.90   $15.90  
  Purchase #4 $164.89   4.342%   $172.0495   $172.05   $172.05   $172.00  
  Purchase #5 $58.35   9.649%   $63.9802   $63.98   $64.00   $64.00  
  Purchase #6 $10.77   13.619%   $12.2368   $12.24   $12.25   $12.20  
  Purchase #7 $163.69   9.452%   $179.162   $179.16   $179.15   $179.20  
  7 purchase totals = $878.54       $964.9826   $964.98   $965.05   $965.00