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 $146.46   11.623%   $163.483   $163.48   $163.50   $163.50  
  Purchase #2 $31.36   11.804%   $35.0617   $35.06   $35.05   $35.10  
  Purchase #3 $112.80   13.211%   $127.702   $127.70   $127.70   $127.70  
  Purchase #4 $42.71   4.853%   $44.7827   $44.78   $44.80   $44.80  
  Purchase #5 $27.97   10.394%   $30.8772   $30.88   $30.90   $30.90  
  Purchase #6 $157.39   12.854%   $177.6209   $177.62   $177.60   $177.60  
  Purchase #7 $156.54   7.370%   $168.077   $168.08   $168.10   $168.10  
  7 purchase totals = $675.23       $747.6045   $747.60   $747.65   $747.70