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 $191.34   12.485%   $215.2288   $215.23   $215.25   $215.20  
  Purchase #2 $30.53   10.345%   $33.6883   $33.69   $33.70   $33.70  
  Purchase #3 $25.31   3.870%   $26.2895   $26.29   $26.30   $26.30  
  Purchase #4 $248.79   7.146%   $266.5685   $266.57   $266.55   $266.60  
  Purchase #5 $229.47   8.110%   $248.08   $248.08   $248.10   $248.10  
  Purchase #6 $57.64   4.393%   $60.1721   $60.17   $60.15   $60.20  
  Purchase #7 $119.93   13.412%   $136.015   $136.02   $136.00   $136.00  
  7 purchase totals = $903.01       $986.0422   $986.05   $986.05   $986.10