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 $14.43   12.560%   $16.2424   $16.24   $16.25   $16.20  
  Purchase #2 $97.55   7.244%   $104.6165   $104.62   $104.60   $104.60  
  Purchase #3 $147.57   5.726%   $156.0199   $156.02   $156.00   $156.00  
  Purchase #4 $186.93   6.665%   $199.3889   $199.39   $199.40   $199.40  
  Purchase #5 $68.78   6.741%   $73.4165   $73.42   $73.40   $73.40  
  Purchase #6 $146.26   11.175%   $162.6046   $162.60   $162.60   $162.60  
  Purchase #7 $111.83   10.620%   $123.7063   $123.71   $123.70   $123.70  
  7 purchase totals = $773.35       $835.9951   $836.00   $835.95   $835.90