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 $69.77   10.258%   $76.927   $76.93   $76.95   $76.90  
  Purchase #2 $171.69   9.396%   $187.822   $187.82   $187.80   $187.80  
  Purchase #3 $58.77   13.413%   $66.6528   $66.65   $66.65   $66.70  
  Purchase #4 $43.55   7.830%   $46.96   $46.96   $46.95   $47.00  
  Purchase #5 $113.62   7.574%   $122.2256   $122.23   $122.25   $122.20  
  Purchase #6 $99.95   11.542%   $111.4862   $111.49   $111.50   $111.50  
  Purchase #7 $185.73   13.294%   $210.4209   $210.42   $210.40   $210.40  
  7 purchase totals = $743.08       $822.4945   $822.50   $822.50   $822.50