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 $61.59   8.750%   $66.9791   $66.98   $67.00   $67.00  
  Purchase #2 $156.77   13.151%   $177.3868   $177.39   $177.40   $177.40  
  Purchase #3 $22.48   10.113%   $24.7534   $24.75   $24.75   $24.80  
  Purchase #4 $103.67   4.406%   $108.2377   $108.24   $108.25   $108.20  
  Purchase #5 $8.67   9.251%   $9.4721   $9.47   $9.45   $9.50  
  Purchase #6 $166.45   7.521%   $178.9687   $178.97   $178.95   $179.00  
  Purchase #7 $217.86   6.326%   $231.6418   $231.64   $231.65   $231.60  
  7 purchase totals = $737.49       $797.4396   $797.44   $797.45   $797.50