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 $85.84   13.112%   $97.0953   $97.10   $97.10   $97.10  
  Purchase #2 $223.47   4.309%   $233.0993   $233.10   $233.10   $233.10  
  Purchase #3 $53.72   13.866%   $61.1688   $61.17   $61.15   $61.20  
  Purchase #4 $131.45   4.174%   $136.9367   $136.94   $136.95   $136.90  
  Purchase #5 $6.30   9.742%   $6.9137   $6.91   $6.90   $6.90  
  Purchase #6 $242.91   4.217%   $253.1535   $253.15   $253.15   $253.20  
  Purchase #7 $30.58   11.613%   $34.1313   $34.13   $34.15   $34.10  
  7 purchase totals = $774.27       $822.4986   $822.50   $822.50   $822.50