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 $94.82   6.636%   $101.1123   $101.11   $101.10   $101.10  
  Purchase #2 $218.79   13.135%   $247.5281   $247.53   $247.55   $247.50  
  Purchase #3 $196.93   5.762%   $208.2771   $208.28   $208.30   $208.30  
  Purchase #4 $70.49   8.814%   $76.703   $76.70   $76.70   $76.70  
  Purchase #5 $148.42   9.610%   $162.6832   $162.68   $162.70   $162.70  
  Purchase #6 $215.54   13.688%   $245.0431   $245.04   $245.05   $245.00  
  Purchase #7 $20.62   8.330%   $22.3376   $22.34   $22.35   $22.30  
  7 purchase totals = $965.61       $1,063.6844   $1,063.68   $1,063.75   $1,063.60