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 $244.84   12.534%   $275.5282   $275.53   $275.55   $275.50  
  Purchase #2 $203.25   7.122%   $217.7255   $217.73   $217.75   $217.70  
  Purchase #3 $87.31   13.658%   $99.2348   $99.23   $99.25   $99.20  
  Purchase #4 $244.76   5.602%   $258.4715   $258.47   $258.45   $258.50  
  Purchase #5 $244.47   13.545%   $277.5835   $277.58   $277.60   $277.60  
  Purchase #6 $213.76   5.661%   $225.861   $225.86   $225.85   $225.90  
  Purchase #7 $90.58   5.123%   $95.2204   $95.22   $95.20   $95.20  
  7 purchase totals = $1,328.97       $1,449.6249   $1,449.62   $1,449.65   $1,449.60