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 $126.78   13.575%   $143.9904   $143.99   $144.00   $144.00  
  Purchase #2 $53.69   4.716%   $56.222   $56.22   $56.20   $56.20  
  Purchase #3 $65.57   8.739%   $71.3002   $71.30   $71.30   $71.30  
  Purchase #4 $233.45   12.750%   $263.2149   $263.21   $263.20   $263.20  
  Purchase #5 $125.99   8.641%   $136.8768   $136.88   $136.90   $136.90  
  Purchase #6 $144.41   10.568%   $159.6712   $159.67   $159.65   $159.70  
  Purchase #7 $59.68   8.390%   $64.6872   $64.69   $64.70   $64.70  
  7 purchase totals = $809.57       $895.9627   $895.96   $895.95   $896.00