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 $206.92   7.782%   $223.0225   $223.02   $223.00   $223.00  
  Purchase #2 $136.49   12.729%   $153.8638   $153.86   $153.85   $153.90  
  Purchase #3 $177.48   12.423%   $199.5283   $199.53   $199.55   $199.50  
  Purchase #4 $119.89   3.455%   $124.0322   $124.03   $124.05   $124.00  
  Purchase #5 $186.88   3.821%   $194.0207   $194.02   $194.00   $194.00  
  Purchase #6 $201.91   12.244%   $226.6319   $226.63   $226.65   $226.60  
  Purchase #7 $174.91   11.296%   $194.6678   $194.67   $194.65   $194.70  
  7 purchase totals = $1,204.48       $1,315.7672   $1,315.76   $1,315.75   $1,315.70