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 $235.48   13.543%   $267.3711   $267.37   $267.35   $267.40  
  Purchase #2 $43.86   12.472%   $49.3302   $49.33   $49.35   $49.30  
  Purchase #3 $173.58   7.731%   $186.9995   $187.00   $187.00   $187.00  
  Purchase #4 $81.65   5.500%   $86.1408   $86.14   $86.15   $86.10  
  Purchase #5 $18.97   12.579%   $21.3562   $21.36   $21.35   $21.40  
  Purchase #6 $97.69   7.465%   $104.9826   $104.98   $105.00   $105.00  
  Purchase #7 $180.49   5.338%   $190.1246   $190.12   $190.10   $190.10  
  7 purchase totals = $831.72       $906.3050   $906.30   $906.30   $906.30