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 $237.44   6.212%   $252.1898   $252.19   $252.20   $252.20  
  Purchase #2 $201.90   5.412%   $212.8268   $212.83   $212.85   $212.80  
  Purchase #3 $125.89   4.853%   $131.9994   $132.00   $132.00   $132.00  
  Purchase #4 $193.83   3.525%   $200.6625   $200.66   $200.65   $200.70  
  Purchase #5 $158.75   8.717%   $172.5882   $172.59   $172.60   $172.60  
  Purchase #6 $14.40   12.473%   $16.1961   $16.20   $16.20   $16.20  
  Purchase #7 $14.69   3.194%   $15.1592   $15.16   $15.15   $15.20  
  7 purchase totals = $946.90       $1,001.6220   $1,001.63   $1,001.65   $1,001.70