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 $215.47   5.511%   $227.3446   $227.34   $227.35   $227.30  
  Purchase #2 $32.79   6.837%   $35.0319   $35.03   $35.05   $35.00  
  Purchase #3 $54.29   10.627%   $60.0594   $60.06   $60.05   $60.10  
  Purchase #4 $127.69   6.835%   $136.4176   $136.42   $136.40   $136.40  
  Purchase #5 $59.34   5.665%   $62.7016   $62.70   $62.70   $62.70  
  Purchase #6 $71.87   3.706%   $74.5335   $74.53   $74.55   $74.50  
  Purchase #7 $159.50   3.129%   $164.4908   $164.49   $164.50   $164.50  
  7 purchase totals = $720.95       $760.5794   $760.57   $760.60   $760.50