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 $115.75   6.412%   $123.1719   $123.17   $123.15   $123.20  
  Purchase #2 $50.98   10.499%   $56.3324   $56.33   $56.35   $56.30  
  Purchase #3 $65.98   7.779%   $71.1126   $71.11   $71.10   $71.10  
  Purchase #4 $184.91   4.747%   $193.6877   $193.69   $193.70   $193.70  
  Purchase #5 $194.57   7.385%   $208.939   $208.94   $208.95   $208.90  
  Purchase #6 $156.76   10.333%   $172.958   $172.96   $172.95   $173.00  
  Purchase #7 $118.42   10.613%   $130.9879   $130.99   $131.00   $131.00  
  7 purchase totals = $887.37       $957.1895   $957.19   $957.20   $957.20