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 $55.28   11.673%   $61.7328   $61.73   $61.75   $61.70  
  Purchase #2 $233.25   9.580%   $255.5954   $255.60   $255.60   $255.60  
  Purchase #3 $124.85   7.158%   $133.7868   $133.79   $133.80   $133.80  
  Purchase #4 $144.55   12.522%   $162.6506   $162.65   $162.65   $162.70  
  Purchase #5 $13.46   3.782%   $13.9691   $13.97   $13.95   $14.00  
  Purchase #6 $48.35   5.455%   $50.9875   $50.99   $51.00   $51.00  
  Purchase #7 $6.90   8.331%   $7.4748   $7.47   $7.45   $7.50  
  7 purchase totals = $626.64       $686.1970   $686.20   $686.20   $686.30