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 $208.48   6.301%   $221.6163   $221.62   $221.60   $221.60  
  Purchase #2 $35.42   8.699%   $38.5012   $38.50   $38.50   $38.50  
  Purchase #3 $226.81   8.103%   $245.1884   $245.19   $245.20   $245.20  
  Purchase #4 $56.87   5.190%   $59.8216   $59.82   $59.80   $59.80  
  Purchase #5 $53.60   7.582%   $57.664   $57.66   $57.65   $57.70  
  Purchase #6 $34.68   3.743%   $35.9781   $35.98   $36.00   $36.00  
  Purchase #7 $230.28   6.409%   $245.0386   $245.04   $245.05   $245.00  
  7 purchase totals = $846.14       $903.8082   $903.81   $903.80   $903.80