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 $58.30   8.503%   $63.2572   $63.26   $63.25   $63.30  
  Purchase #2 $204.75   11.482%   $228.2594   $228.26   $228.25   $228.30  
  Purchase #3 $217.46   5.243%   $228.8614   $228.86   $228.85   $228.90  
  Purchase #4 $59.83   9.695%   $65.6305   $65.63   $65.65   $65.60  
  Purchase #5 $102.27   4.493%   $106.865   $106.87   $106.85   $106.90  
  Purchase #6 $7.62   12.685%   $8.5866   $8.59   $8.60   $8.60  
  Purchase #7 $247.42   9.472%   $270.8556   $270.86   $270.85   $270.90  
  7 purchase totals = $897.65       $972.3157   $972.33   $972.30   $972.50