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 $35.31   6.504%   $37.6066   $37.61   $37.60   $37.60  
  Purchase #2 $211.39   13.763%   $240.4836   $240.48   $240.50   $240.50  
  Purchase #3 $159.36   6.478%   $169.6833   $169.68   $169.70   $169.70  
  Purchase #4 $24.71   6.526%   $26.3226   $26.32   $26.30   $26.30  
  Purchase #5 $89.82   5.657%   $94.9011   $94.90   $94.90   $94.90  
  Purchase #6 $176.38   4.800%   $184.8462   $184.85   $184.85   $184.80  
  Purchase #7 $134.44   11.189%   $149.4825   $149.48   $149.50   $149.50  
  7 purchase totals = $831.41       $903.3259   $903.32   $903.35   $903.30