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 $231.80   5.454%   $244.4424   $244.44   $244.45   $244.40  
  Purchase #2 $250.81   4.705%   $262.6106   $262.61   $262.60   $262.60  
  Purchase #3 $118.77   6.517%   $126.5102   $126.51   $126.50   $126.50  
  Purchase #4 $134.87   12.392%   $151.5831   $151.58   $151.60   $151.60  
  Purchase #5 $10.92   8.495%   $11.8477   $11.85   $11.85   $11.80  
  Purchase #6 $181.77   8.390%   $197.0205   $197.02   $197.00   $197.00  
  Purchase #7 $28.79   5.116%   $30.2629   $30.26   $30.25   $30.30  
  7 purchase totals = $957.73       $1,024.2774   $1,024.27   $1,024.25   $1,024.20