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 $202.66   12.797%   $228.5944   $228.59   $228.60   $228.60  
  Purchase #2 $151.66   10.138%   $167.0353   $167.04   $167.05   $167.00  
  Purchase #3 $11.62   8.845%   $12.6478   $12.65   $12.65   $12.60  
  Purchase #4 $12.67   10.369%   $13.9838   $13.98   $14.00   $14.00  
  Purchase #5 $54.80   6.715%   $58.4798   $58.48   $58.50   $58.50  
  Purchase #6 $231.95   4.187%   $241.6617   $241.66   $241.65   $241.70  
  Purchase #7 $98.46   3.874%   $102.2743   $102.27   $102.25   $102.30  
  7 purchase totals = $763.82       $824.6771   $824.67   $824.70   $824.70