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 $248.92   5.674%   $263.0437   $263.04   $263.05   $263.00  
  Purchase #2 $173.90   12.181%   $195.0828   $195.08   $195.10   $195.10  
  Purchase #3 $41.61   3.826%   $43.202   $43.20   $43.20   $43.20  
  Purchase #4 $115.74   6.144%   $122.8511   $122.85   $122.85   $122.90  
  Purchase #5 $136.70   9.233%   $149.3215   $149.32   $149.30   $149.30  
  Purchase #6 $58.38   13.719%   $66.3892   $66.39   $66.40   $66.40  
  Purchase #7 $240.76   6.250%   $255.8075   $255.81   $255.80   $255.80  
  7 purchase totals = $1,016.01       $1,095.6978   $1,095.69   $1,095.70   $1,095.70