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 $60.38   7.743%   $65.0552   $65.06   $65.05   $65.10  
  Purchase #2 $207.29   5.676%   $219.0558   $219.06   $219.05   $219.10  
  Purchase #3 $242.60   3.826%   $251.8819   $251.88   $251.90   $251.90  
  Purchase #4 $208.83   12.404%   $234.7333   $234.73   $234.75   $234.70  
  Purchase #5 $90.79   8.520%   $98.5253   $98.53   $98.55   $98.50  
  Purchase #6 $70.74   7.480%   $76.0314   $76.03   $76.05   $76.00  
  Purchase #7 $6.65   9.540%   $7.2844   $7.28   $7.30   $7.30  
  7 purchase totals = $887.28       $952.5673   $952.57   $952.65   $952.60