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 $106.91   12.155%   $119.9049   $119.90   $119.90   $119.90  
  Purchase #2 $109.65   7.352%   $117.7115   $117.71   $117.70   $117.70  
  Purchase #3 $67.91   5.604%   $71.7157   $71.72   $71.70   $71.70  
  Purchase #4 $164.46   7.407%   $176.6416   $176.64   $176.65   $176.60  
  Purchase #5 $207.89   12.508%   $233.8929   $233.89   $233.90   $233.90  
  Purchase #6 $51.78   13.509%   $58.775   $58.78   $58.80   $58.80  
  Purchase #7 $187.34   13.616%   $212.8482   $212.85   $212.85   $212.80  
  7 purchase totals = $895.94       $991.4898   $991.49   $991.50   $991.40