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 $217.68   11.688%   $243.1224   $243.12   $243.10   $243.10  
  Purchase #2 $50.92   11.549%   $56.8008   $56.80   $56.80   $56.80  
  Purchase #3 $16.71   9.308%   $18.2654   $18.27   $18.25   $18.30  
  Purchase #4 $163.72   6.141%   $173.774   $173.77   $173.75   $173.80  
  Purchase #5 $119.85   9.426%   $131.1471   $131.15   $131.15   $131.10  
  Purchase #6 $186.50   4.110%   $194.1652   $194.17   $194.15   $194.20  
  Purchase #7 $209.48   12.149%   $234.9297   $234.93   $234.95   $234.90  
  7 purchase totals = $964.86       $1,052.2046   $1,052.21   $1,052.15   $1,052.20