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 $196.42   9.578%   $215.2331   $215.23   $215.25   $215.20  
  Purchase #2 $103.73   13.657%   $117.8964   $117.90   $117.90   $117.90  
  Purchase #3 $42.56   4.699%   $44.5599   $44.56   $44.55   $44.60  
  Purchase #4 $59.36   7.749%   $63.9598   $63.96   $63.95   $64.00  
  Purchase #5 $197.26   11.225%   $219.4024   $219.40   $219.40   $219.40  
  Purchase #6 $211.95   13.115%   $239.7472   $239.75   $239.75   $239.70  
  Purchase #7 $53.83   9.764%   $59.086   $59.09   $59.10   $59.10  
  7 purchase totals = $865.11       $959.8848   $959.89   $959.90   $959.90