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 $76.52   11.337%   $85.1951   $85.20   $85.20   $85.20  
  Purchase #2 $17.58   10.836%   $19.485   $19.49   $19.50   $19.50  
  Purchase #3 $85.28   13.731%   $96.9898   $96.99   $97.00   $97.00  
  Purchase #4 $219.36   4.705%   $229.6809   $229.68   $229.70   $229.70  
  Purchase #5 $66.76   6.384%   $71.022   $71.02   $71.00   $71.00  
  Purchase #6 $217.93   10.762%   $241.3836   $241.38   $241.40   $241.40  
  Purchase #7 $30.92   11.445%   $34.4588   $34.46   $34.45   $34.50  
  7 purchase totals = $714.35       $778.2152   $778.22   $778.25   $778.30