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 $243.61   8.593%   $264.5434   $264.54   $264.55   $264.50  
  Purchase #2 $137.86   8.162%   $149.1121   $149.11   $149.10   $149.10  
  Purchase #3 $250.89   7.153%   $268.8362   $268.84   $268.85   $268.80  
  Purchase #4 $149.51   9.215%   $163.2873   $163.29   $163.30   $163.30  
  Purchase #5 $215.90   6.473%   $229.8752   $229.88   $229.90   $229.90  
  Purchase #6 $51.58   9.309%   $56.3816   $56.38   $56.40   $56.40  
  Purchase #7 $159.70   9.222%   $174.4275   $174.43   $174.45   $174.40  
  7 purchase totals = $1,209.05       $1,306.4633   $1,306.47   $1,306.55   $1,306.40