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 $95.40   3.121%   $98.3774   $98.38   $98.40   $98.40  
  Purchase #2 $204.76   12.844%   $231.0594   $231.06   $231.05   $231.10  
  Purchase #3 $60.48   13.627%   $68.7216   $68.72   $68.70   $68.70  
  Purchase #4 $91.94   6.175%   $97.6173   $97.62   $97.60   $97.60  
  Purchase #5 $223.71   5.357%   $235.6941   $235.69   $235.70   $235.70  
  Purchase #6 $65.83   4.216%   $68.6054   $68.61   $68.60   $68.60  
  Purchase #7 $215.89   3.143%   $222.6754   $222.68   $222.70   $222.70  
  7 purchase totals = $958.01       $1,022.7506   $1,022.76   $1,022.75   $1,022.80