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 $227.25   10.792%   $251.7748   $251.77   $251.75   $251.80  
  Purchase #2 $91.59   5.422%   $96.556   $96.56   $96.55   $96.60  
  Purchase #3 $123.39   8.136%   $133.429   $133.43   $133.45   $133.40  
  Purchase #4 $209.61   13.115%   $237.1004   $237.10   $237.10   $237.10  
  Purchase #5 $49.86   3.372%   $51.5413   $51.54   $51.55   $51.50  
  Purchase #6 $63.45   4.243%   $66.1422   $66.14   $66.15   $66.10  
  Purchase #7 $244.70   5.678%   $258.5941   $258.59   $258.60   $258.60  
  7 purchase totals = $1,009.85       $1,095.1378   $1,095.13   $1,095.15   $1,095.10