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 $226.62   8.580%   $246.064   $246.06   $246.05   $246.10  
  Purchase #2 $87.38   11.525%   $97.4505   $97.45   $97.45   $97.50  
  Purchase #3 $19.88   10.680%   $22.0032   $22.00   $22.00   $22.00  
  Purchase #4 $228.81   5.795%   $242.0695   $242.07   $242.05   $242.10  
  Purchase #5 $249.63   10.643%   $276.1981   $276.20   $276.20   $276.20  
  Purchase #6 $231.88   4.651%   $242.6647   $242.66   $242.65   $242.70  
  Purchase #7 $176.53   5.480%   $186.2038   $186.20   $186.20   $186.20  
  7 purchase totals = $1,220.73       $1,312.6538   $1,312.64   $1,312.60   $1,312.80