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 $68.47   4.212%   $71.354   $71.35   $71.35   $71.40  
  Purchase #2 $76.62   4.276%   $79.8963   $79.90   $79.90   $79.90  
  Purchase #3 $60.34   5.186%   $63.4692   $63.47   $63.45   $63.50  
  Purchase #4 $247.54   6.616%   $263.9172   $263.92   $263.90   $263.90  
  Purchase #5 $60.43   8.574%   $65.6113   $65.61   $65.60   $65.60  
  Purchase #6 $12.95   4.757%   $13.566   $13.57   $13.55   $13.60  
  Purchase #7 $52.48   6.777%   $56.0366   $56.04   $56.05   $56.00  
  7 purchase totals = $578.83       $613.8506   $613.86   $613.80   $613.90