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 $62.38   13.246%   $70.6429   $70.64   $70.65   $70.60  
  Purchase #2 $240.65   7.138%   $257.8276   $257.83   $257.85   $257.80  
  Purchase #3 $95.73   7.562%   $102.9691   $102.97   $102.95   $103.00  
  Purchase #4 $208.92   3.378%   $215.9773   $215.98   $216.00   $216.00  
  Purchase #5 $112.81   4.556%   $117.9496   $117.95   $117.95   $117.90  
  Purchase #6 $125.71   7.148%   $134.6958   $134.70   $134.70   $134.70  
  Purchase #7 $143.33   7.661%   $154.3105   $154.31   $154.30   $154.30  
  7 purchase totals = $989.53       $1,054.3728   $1,054.38   $1,054.40   $1,054.30