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 $53.48   13.241%   $60.5613   $60.56   $60.55   $60.60  
  Purchase #2 $90.52   7.157%   $96.9985   $97.00   $97.00   $97.00  
  Purchase #3 $187.58   11.450%   $209.0579   $209.06   $209.05   $209.10  
  Purchase #4 $60.51   10.677%   $66.9707   $66.97   $66.95   $67.00  
  Purchase #5 $36.26   12.628%   $40.8389   $40.84   $40.85   $40.80  
  Purchase #6 $192.42   11.189%   $213.9499   $213.95   $213.95   $213.90  
  Purchase #7 $26.27   13.430%   $29.7981   $29.80   $29.80   $29.80  
  7 purchase totals = $647.04       $718.1753   $718.18   $718.15   $718.20