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 $200.79   11.473%   $223.8266   $223.83   $223.85   $223.80  
  Purchase #2 $113.92   4.750%   $119.3312   $119.33   $119.35   $119.30  
  Purchase #3 $161.34   8.837%   $175.5976   $175.60   $175.60   $175.60  
  Purchase #4 $191.95   7.775%   $206.8741   $206.87   $206.85   $206.90  
  Purchase #5 $78.70   4.819%   $82.4926   $82.49   $82.50   $82.50  
  Purchase #6 $91.70   10.600%   $101.4202   $101.42   $101.40   $101.40  
  Purchase #7 $45.26   12.269%   $50.8129   $50.81   $50.80   $50.80  
  7 purchase totals = $883.66       $960.3552   $960.35   $960.35   $960.30