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 $171.78   6.108%   $182.2723   $182.27   $182.25   $182.30  
  Purchase #2 $169.64   12.394%   $190.6652   $190.67   $190.65   $190.70  
  Purchase #3 $208.66   13.120%   $236.0362   $236.04   $236.05   $236.00  
  Purchase #4 $51.65   13.111%   $58.4218   $58.42   $58.40   $58.40  
  Purchase #5 $217.88   6.177%   $231.3384   $231.34   $231.35   $231.30  
  Purchase #6 $44.33   11.131%   $49.2644   $49.26   $49.25   $49.30  
  Purchase #7 $200.79   11.578%   $224.0375   $224.04   $224.05   $224.00  
  7 purchase totals = $1,064.73       $1,172.0358   $1,172.04   $1,172.00   $1,172.00