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 $34.46   6.287%   $36.6265   $36.63   $36.65   $36.60  
  Purchase #2 $14.78   13.464%   $16.77   $16.77   $16.75   $16.80  
  Purchase #3 $21.48   11.134%   $23.8716   $23.87   $23.85   $23.90  
  Purchase #4 $231.87   12.477%   $260.8004   $260.80   $260.80   $260.80  
  Purchase #5 $183.35   13.140%   $207.4422   $207.44   $207.45   $207.40  
  Purchase #6 $167.87   9.169%   $183.262   $183.26   $183.25   $183.30  
  Purchase #7 $244.74   9.859%   $268.8689   $268.87   $268.85   $268.90  
  7 purchase totals = $898.55       $997.6416   $997.64   $997.60   $997.70