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 $143.95   13.372%   $163.199   $163.20   $163.20   $163.20  
  Purchase #2 $189.69   5.361%   $199.8593   $199.86   $199.85   $199.90  
  Purchase #3 $220.66   7.201%   $236.5497   $236.55   $236.55   $236.50  
  Purchase #4 $229.99   3.371%   $237.743   $237.74   $237.75   $237.70  
  Purchase #5 $164.55   7.742%   $177.2895   $177.29   $177.30   $177.30  
  Purchase #6 $10.51   11.538%   $11.7226   $11.72   $11.70   $11.70  
  Purchase #7 $64.56   8.227%   $69.8714   $69.87   $69.85   $69.90  
  7 purchase totals = $1,023.91       $1,096.2345   $1,096.23   $1,096.20   $1,096.20