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 $117.82   8.239%   $127.5272   $127.53   $127.55   $127.50  
  Purchase #2 $47.26   5.821%   $50.011   $50.01   $50.00   $50.00  
  Purchase #3 $148.84   6.772%   $158.9194   $158.92   $158.90   $158.90  
  Purchase #4 $214.98   12.695%   $242.2717   $242.27   $242.25   $242.30  
  Purchase #5 $176.98   9.257%   $193.363   $193.36   $193.35   $193.40  
  Purchase #6 $124.61   5.664%   $131.6679   $131.67   $131.65   $131.70  
  Purchase #7 $192.49   8.676%   $209.1904   $209.19   $209.20   $209.20  
  7 purchase totals = $1,022.98       $1,112.9506   $1,112.95   $1,112.90   $1,113.00