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 $100.27   9.157%   $109.4517   $109.45   $109.45   $109.50  
  Purchase #2 $78.41   13.767%   $89.2047   $89.20   $89.20   $89.20  
  Purchase #3 $93.36   13.650%   $106.1036   $106.10   $106.10   $106.10  
  Purchase #4 $50.89   6.428%   $54.1612   $54.16   $54.15   $54.20  
  Purchase #5 $9.40   3.425%   $9.722   $9.72   $9.70   $9.70  
  Purchase #6 $245.83   10.103%   $270.6662   $270.67   $270.65   $270.70  
  Purchase #7 $70.49   9.726%   $77.3459   $77.35   $77.35   $77.30  
  7 purchase totals = $648.65       $716.6553   $716.65   $716.60   $716.70