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 $191.96   8.506%   $208.2881   $208.29   $208.30   $208.30  
  Purchase #2 $149.78   12.593%   $168.6418   $168.64   $168.65   $168.60  
  Purchase #3 $113.82   3.259%   $117.5294   $117.53   $117.55   $117.50  
  Purchase #4 $43.58   11.540%   $48.6091   $48.61   $48.60   $48.60  
  Purchase #5 $194.26   5.491%   $204.9268   $204.93   $204.95   $204.90  
  Purchase #6 $226.31   11.128%   $251.4938   $251.49   $251.50   $251.50  
  Purchase #7 $7.66   9.590%   $8.3946   $8.39   $8.40   $8.40  
  7 purchase totals = $927.37       $1,007.8836   $1,007.88   $1,007.95   $1,007.80