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 $242.26   7.398%   $260.1824   $260.18   $260.20   $260.20  
  Purchase #2 $232.71   6.364%   $247.5197   $247.52   $247.50   $247.50  
  Purchase #3 $86.57   13.496%   $98.2535   $98.25   $98.25   $98.30  
  Purchase #4 $56.34   11.675%   $62.9177   $62.92   $62.90   $62.90  
  Purchase #5 $186.44   4.833%   $195.4506   $195.45   $195.45   $195.50  
  Purchase #6 $161.66   10.234%   $178.2043   $178.20   $178.20   $178.20  
  Purchase #7 $25.95   3.163%   $26.7708   $26.77   $26.75   $26.80  
  7 purchase totals = $991.93       $1,069.2990   $1,069.29   $1,069.25   $1,069.40