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 $81.36   9.864%   $89.3854   $89.39   $89.40   $89.40  
  Purchase #2 $41.96   4.256%   $43.7458   $43.75   $43.75   $43.70  
  Purchase #3 $27.62   7.744%   $29.7589   $29.76   $29.75   $29.80  
  Purchase #4 $214.68   5.539%   $226.5711   $226.57   $226.55   $226.60  
  Purchase #5 $17.73   8.315%   $19.2042   $19.20   $19.20   $19.20  
  Purchase #6 $158.25   3.241%   $163.3789   $163.38   $163.40   $163.40  
  Purchase #7 $39.58   10.826%   $43.8649   $43.86   $43.85   $43.90  
  7 purchase totals = $581.18       $615.9092   $615.91   $615.90   $616.00