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 $66.78   11.207%   $74.264   $74.26   $74.25   $74.30  
  Purchase #2 $215.96   3.619%   $223.7756   $223.78   $223.80   $223.80  
  Purchase #3 $118.95   3.167%   $122.7171   $122.72   $122.70   $122.70  
  Purchase #4 $247.71   4.342%   $258.4656   $258.47   $258.45   $258.50  
  Purchase #5 $21.63   6.437%   $23.0223   $23.02   $23.00   $23.00  
  Purchase #6 $69.47   4.354%   $72.4947   $72.49   $72.50   $72.50  
  Purchase #7 $117.61   13.545%   $133.5403   $133.54   $133.55   $133.50  
  7 purchase totals = $858.11       $908.2796   $908.28   $908.25   $908.30