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 $116.95   8.571%   $126.9738   $126.97   $126.95   $127.00  
  Purchase #2 $50.68   3.520%   $52.4639   $52.46   $52.45   $52.50  
  Purchase #3 $97.52   3.246%   $100.6855   $100.69   $100.70   $100.70  
  Purchase #4 $166.41   3.638%   $172.464   $172.46   $172.45   $172.50  
  Purchase #5 $118.40   9.326%   $129.442   $129.44   $129.45   $129.40  
  Purchase #6 $112.91   10.603%   $124.8818   $124.88   $124.90   $124.90  
  Purchase #7 $130.57   4.748%   $136.7695   $136.77   $136.75   $136.80  
  7 purchase totals = $793.44       $843.6805   $843.67   $843.65   $843.80