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 $211.73   11.864%   $236.8496   $236.85   $236.85   $236.80  
  Purchase #2 $10.63   7.245%   $11.4001   $11.40   $11.40   $11.40  
  Purchase #3 $92.37   4.617%   $96.6347   $96.63   $96.65   $96.60  
  Purchase #4 $98.47   11.612%   $109.9043   $109.90   $109.90   $109.90  
  Purchase #5 $59.70   6.569%   $63.6217   $63.62   $63.60   $63.60  
  Purchase #6 $181.78   6.189%   $193.0304   $193.03   $193.05   $193.00  
  Purchase #7 $65.84   10.141%   $72.5168   $72.52   $72.50   $72.50  
  7 purchase totals = $720.52       $783.9576   $783.95   $783.95   $783.80