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 $93.79   3.609%   $97.1749   $97.17   $97.15   $97.20  
  Purchase #2 $70.32   4.203%   $73.2755   $73.28   $73.30   $73.30  
  Purchase #3 $13.52   13.476%   $15.342   $15.34   $15.35   $15.30  
  Purchase #4 $239.44   6.663%   $255.3939   $255.39   $255.40   $255.40  
  Purchase #5 $193.60   9.277%   $211.5603   $211.56   $211.55   $211.60  
  Purchase #6 $159.81   7.337%   $171.5353   $171.54   $171.55   $171.50  
  Purchase #7 $125.60   7.301%   $134.7701   $134.77   $134.75   $134.80  
  7 purchase totals = $896.08       $959.0520   $959.05   $959.05   $959.10