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 $142.86   13.634%   $162.3375   $162.34   $162.35   $162.30  
  Purchase #2 $214.66   10.752%   $237.7402   $237.74   $237.75   $237.70  
  Purchase #3 $11.90   13.147%   $13.4645   $13.46   $13.45   $13.50  
  Purchase #4 $141.80   7.216%   $152.0323   $152.03   $152.05   $152.00  
  Purchase #5 $73.77   10.709%   $81.67   $81.67   $81.65   $81.70  
  Purchase #6 $174.94   10.631%   $193.5379   $193.54   $193.55   $193.50  
  Purchase #7 $163.60   3.820%   $169.8495   $169.85   $169.85   $169.80  
  7 purchase totals = $923.53       $1,010.6319   $1,010.63   $1,010.65   $1,010.50