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 $92.28   6.481%   $98.2607   $98.26   $98.25   $98.30  
  Purchase #2 $123.26   10.801%   $136.5733   $136.57   $136.55   $136.60  
  Purchase #3 $42.37   6.628%   $45.1783   $45.18   $45.20   $45.20  
  Purchase #4 $60.42   9.698%   $66.2795   $66.28   $66.30   $66.30  
  Purchase #5 $141.80   8.532%   $153.8984   $153.90   $153.90   $153.90  
  Purchase #6 $119.83   5.116%   $125.9605   $125.96   $125.95   $126.00  
  Purchase #7 $72.86   6.356%   $77.491   $77.49   $77.50   $77.50  
  7 purchase totals = $652.82       $703.6417   $703.64   $703.65   $703.80