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 $65.81   3.407%   $68.0521   $68.05   $68.05   $68.10  
  Purchase #2 $32.75   10.854%   $36.3047   $36.30   $36.30   $36.30  
  Purchase #3 $110.71   7.319%   $118.8129   $118.81   $118.80   $118.80  
  Purchase #4 $151.41   8.250%   $163.9013   $163.90   $163.90   $163.90  
  Purchase #5 $56.62   3.459%   $58.5785   $58.58   $58.60   $58.60  
  Purchase #6 $207.47   10.540%   $229.3373   $229.34   $229.35   $229.30  
  Purchase #7 $79.83   5.142%   $83.9349   $83.93   $83.95   $83.90  
  7 purchase totals = $704.60       $758.9217   $758.91   $758.95   $758.90