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 $249.54   7.650%   $268.6298   $268.63   $268.65   $268.60  
  Purchase #2 $115.30   7.264%   $123.6754   $123.68   $123.70   $123.70  
  Purchase #3 $230.56   7.207%   $247.1765   $247.18   $247.20   $247.20  
  Purchase #4 $22.63   9.413%   $24.7602   $24.76   $24.75   $24.80  
  Purchase #5 $208.46   10.828%   $231.032   $231.03   $231.05   $231.00  
  Purchase #6 $5.35   9.476%   $5.857   $5.86   $5.85   $5.90  
  Purchase #7 $58.99   4.868%   $61.8616   $61.86   $61.85   $61.90  
  7 purchase totals = $890.83       $962.9925   $963.00   $963.05   $963.10