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 $91.46   6.211%   $97.1406   $97.14   $97.15   $97.10  
  Purchase #2 $248.64   11.261%   $276.6394   $276.64   $276.65   $276.60  
  Purchase #3 $112.74   6.641%   $120.2271   $120.23   $120.25   $120.20  
  Purchase #4 $23.82   10.845%   $26.4033   $26.40   $26.40   $26.40  
  Purchase #5 $111.30   13.328%   $126.1341   $126.13   $126.15   $126.10  
  Purchase #6 $115.94   11.469%   $129.2372   $129.24   $129.25   $129.20  
  Purchase #7 $106.95   11.400%   $119.1423   $119.14   $119.15   $119.10  
  7 purchase totals = $810.85       $894.9240   $894.92   $895.00   $894.70