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 $224.76   7.497%   $241.6103   $241.61   $241.60   $241.60  
  Purchase #2 $118.87   10.239%   $131.0411   $131.04   $131.05   $131.00  
  Purchase #3 $65.74   4.810%   $68.9021   $68.90   $68.90   $68.90  
  Purchase #4 $189.69   9.424%   $207.5664   $207.57   $207.55   $207.60  
  Purchase #5 $94.93   4.118%   $98.8392   $98.84   $98.85   $98.80  
  Purchase #6 $95.42   10.518%   $105.4563   $105.46   $105.45   $105.50  
  Purchase #7 $242.64   6.772%   $259.0716   $259.07   $259.05   $259.10  
  7 purchase totals = $1,032.05       $1,112.4870   $1,112.49   $1,112.45   $1,112.50