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 $229.64   5.174%   $241.5216   $241.52   $241.50   $241.50  
  Purchase #2 $62.33   6.652%   $66.4762   $66.48   $66.50   $66.50  
  Purchase #3 $60.98   8.276%   $66.0267   $66.03   $66.05   $66.00  
  Purchase #4 $150.37   6.764%   $160.541   $160.54   $160.55   $160.50  
  Purchase #5 $230.76   7.495%   $248.0555   $248.06   $248.05   $248.10  
  Purchase #6 $34.95   11.329%   $38.9095   $38.91   $38.90   $38.90  
  Purchase #7 $41.36   5.806%   $43.7614   $43.76   $43.75   $43.80  
  7 purchase totals = $810.39       $865.2919   $865.30   $865.30   $865.30