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 $88.54   5.714%   $93.5992   $93.60   $93.60   $93.60  
  Purchase #2 $205.70   4.339%   $214.6253   $214.63   $214.65   $214.60  
  Purchase #3 $63.65   6.184%   $67.5861   $67.59   $67.60   $67.60  
  Purchase #4 $37.31   9.111%   $40.7093   $40.71   $40.70   $40.70  
  Purchase #5 $202.93   10.710%   $224.6638   $224.66   $224.65   $224.70  
  Purchase #6 $157.68   7.643%   $169.7315   $169.73   $169.75   $169.70  
  Purchase #7 $146.85   8.116%   $158.7683   $158.77   $158.75   $158.80  
  7 purchase totals = $902.66       $969.6835   $969.69   $969.70   $969.70