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 $213.27   11.212%   $237.1818   $237.18   $237.20   $237.20  
  Purchase #2 $31.71   11.321%   $35.2999   $35.30   $35.30   $35.30  
  Purchase #3 $69.26   11.451%   $77.191   $77.19   $77.20   $77.20  
  Purchase #4 $240.61   11.616%   $268.5593   $268.56   $268.55   $268.60  
  Purchase #5 $206.68   6.471%   $220.0543   $220.05   $220.05   $220.10  
  Purchase #6 $98.56   11.579%   $109.9723   $109.97   $109.95   $110.00  
  Purchase #7 $141.95   6.686%   $151.4408   $151.44   $151.45   $151.40  
  7 purchase totals = $1,002.04       $1,099.6994   $1,099.69   $1,099.70   $1,099.80