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 $225.26   3.403%   $232.9256   $232.93   $232.95   $232.90  
  Purchase #2 $157.71   3.763%   $163.6446   $163.64   $163.65   $163.60  
  Purchase #3 $142.80   3.829%   $148.2678   $148.27   $148.25   $148.30  
  Purchase #4 $41.98   10.870%   $46.5432   $46.54   $46.55   $46.50  
  Purchase #5 $215.69   13.849%   $245.5609   $245.56   $245.55   $245.60  
  Purchase #6 $231.92   5.214%   $244.0123   $244.01   $244.00   $244.00  
  Purchase #7 $237.53   4.312%   $247.7723   $247.77   $247.75   $247.80  
  7 purchase totals = $1,252.89       $1,328.7267   $1,328.72   $1,328.70   $1,328.70