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 $75.35   9.824%   $82.7524   $82.75   $82.75   $82.80  
  Purchase #2 $70.95   3.331%   $73.3133   $73.31   $73.30   $73.30  
  Purchase #3 $200.48   5.700%   $211.9074   $211.91   $211.90   $211.90  
  Purchase #4 $173.27   5.315%   $182.4793   $182.48   $182.50   $182.50  
  Purchase #5 $186.65   3.512%   $193.2051   $193.21   $193.20   $193.20  
  Purchase #6 $18.73   4.116%   $19.5009   $19.50   $19.50   $19.50  
  Purchase #7 $185.94   5.646%   $196.4382   $196.44   $196.45   $196.40  
  7 purchase totals = $911.37       $959.5966   $959.60   $959.60   $959.60