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 $196.65   10.471%   $217.2412   $217.24   $217.25   $217.20  
  Purchase #2 $5.66   6.799%   $6.0448   $6.04   $6.05   $6.00  
  Purchase #3 $113.60   4.774%   $119.0233   $119.02   $119.00   $119.00  
  Purchase #4 $47.36   6.771%   $50.5667   $50.57   $50.55   $50.60  
  Purchase #5 $46.46   9.233%   $50.7497   $50.75   $50.75   $50.70  
  Purchase #6 $113.59   7.707%   $122.3444   $122.34   $122.35   $122.30  
  Purchase #7 $188.46   6.219%   $200.1803   $200.18   $200.20   $200.20  
  7 purchase totals = $711.78       $766.1504   $766.14   $766.15   $766.00