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 $238.61   3.363%   $246.6345   $246.63   $246.65   $246.60  
  Purchase #2 $97.89   8.495%   $106.2058   $106.21   $106.20   $106.20  
  Purchase #3 $105.85   9.198%   $115.5861   $115.59   $115.60   $115.60  
  Purchase #4 $79.32   7.798%   $85.5054   $85.51   $85.50   $85.50  
  Purchase #5 $173.25   4.870%   $181.6873   $181.69   $181.70   $181.70  
  Purchase #6 $135.72   7.866%   $146.3957   $146.40   $146.40   $146.40  
  Purchase #7 $55.34   5.869%   $58.5879   $58.59   $58.60   $58.60  
  7 purchase totals = $885.98       $940.6027   $940.62   $940.65   $940.60