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 $127.46   11.439%   $142.0401   $142.04   $142.05   $142.00  
  Purchase #2 $215.39   9.652%   $236.1794   $236.18   $236.20   $236.20  
  Purchase #3 $51.36   11.267%   $57.1467   $57.15   $57.15   $57.10  
  Purchase #4 $118.86   10.621%   $131.4841   $131.48   $131.50   $131.50  
  Purchase #5 $140.45   11.617%   $156.7661   $156.77   $156.75   $156.80  
  Purchase #6 $246.70   9.548%   $270.2549   $270.25   $270.25   $270.30  
  Purchase #7 $8.37   11.280%   $9.3141   $9.31   $9.30   $9.30  
  7 purchase totals = $908.59       $1,003.1854   $1,003.18   $1,003.20   $1,003.20