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 $245.94   7.860%   $265.2709   $265.27   $265.25   $265.30  
  Purchase #2 $222.97   13.149%   $252.2883   $252.29   $252.30   $252.30  
  Purchase #3 $56.38   7.760%   $60.7551   $60.76   $60.75   $60.80  
  Purchase #4 $222.73   11.851%   $249.1257   $249.13   $249.15   $249.10  
  Purchase #5 $235.48   13.513%   $267.3004   $267.30   $267.30   $267.30  
  Purchase #6 $87.83   5.697%   $92.8337   $92.83   $92.85   $92.80  
  Purchase #7 $146.93   5.244%   $154.635   $154.64   $154.65   $154.60  
  7 purchase totals = $1,218.26       $1,342.2091   $1,342.22   $1,342.25   $1,342.20