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 $180.53   8.837%   $196.4834   $196.48   $196.50   $196.50  
  Purchase #2 $134.78   7.309%   $144.6311   $144.63   $144.65   $144.60  
  Purchase #3 $66.57   11.651%   $74.3261   $74.33   $74.35   $74.30  
  Purchase #4 $173.67   5.864%   $183.854   $183.85   $183.85   $183.90  
  Purchase #5 $111.90   6.524%   $119.2004   $119.20   $119.20   $119.20  
  Purchase #6 $8.70   12.692%   $9.8042   $9.80   $9.80   $9.80  
  Purchase #7 $170.44   9.418%   $186.492   $186.49   $186.50   $186.50  
  7 purchase totals = $846.59       $914.7912   $914.78   $914.85   $914.80