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 $146.92   8.794%   $159.8401   $159.84   $159.85   $159.80  
  Purchase #2 $43.81   5.821%   $46.3602   $46.36   $46.35   $46.40  
  Purchase #3 $173.48   4.163%   $180.702   $180.70   $180.70   $180.70  
  Purchase #4 $199.99   12.233%   $224.4548   $224.45   $224.45   $224.50  
  Purchase #5 $212.27   7.285%   $227.7339   $227.73   $227.75   $227.70  
  Purchase #6 $175.71   4.527%   $183.6644   $183.66   $183.65   $183.70  
  Purchase #7 $44.75   7.806%   $48.2432   $48.24   $48.25   $48.20  
  7 purchase totals = $996.93       $1,070.9986   $1,070.98   $1,071.00   $1,071.00