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 $59.37   8.729%   $64.5524   $64.55   $64.55   $64.60  
  Purchase #2 $201.64   6.491%   $214.7285   $214.73   $214.75   $214.70  
  Purchase #3 $216.90   4.755%   $227.2136   $227.21   $227.20   $227.20  
  Purchase #4 $42.87   11.800%   $47.9287   $47.93   $47.95   $47.90  
  Purchase #5 $76.73   8.283%   $83.0855   $83.09   $83.10   $83.10  
  Purchase #6 $192.29   4.822%   $201.5622   $201.56   $201.55   $201.60  
  Purchase #7 $189.98   9.840%   $208.674   $208.67   $208.65   $208.70  
  7 purchase totals = $979.78       $1,047.7449   $1,047.74   $1,047.75   $1,047.80