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 $206.58   8.563%   $224.2694   $224.27   $224.25   $224.30  
  Purchase #2 $246.42   6.681%   $262.8833   $262.88   $262.90   $262.90  
  Purchase #3 $224.45   12.533%   $252.5803   $252.58   $252.60   $252.60  
  Purchase #4 $165.38   10.224%   $182.2885   $182.29   $182.30   $182.30  
  Purchase #5 $222.52   4.171%   $231.8013   $231.80   $231.80   $231.80  
  Purchase #6 $154.83   8.212%   $167.5446   $167.54   $167.55   $167.50  
  Purchase #7 $26.63   3.228%   $27.4896   $27.49   $27.50   $27.50  
  7 purchase totals = $1,246.81       $1,348.8570   $1,348.85   $1,348.90   $1,348.90