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 $225.56   10.263%   $248.7092   $248.71   $248.70   $248.70  
  Purchase #2 $188.67   8.584%   $204.8654   $204.87   $204.85   $204.90  
  Purchase #3 $14.40   3.504%   $14.9046   $14.90   $14.90   $14.90  
  Purchase #4 $108.97   12.225%   $122.2916   $122.29   $122.30   $122.30  
  Purchase #5 $189.87   13.455%   $215.417   $215.42   $215.40   $215.40  
  Purchase #6 $108.55   5.846%   $114.8958   $114.90   $114.90   $114.90  
  Purchase #7 $156.83   13.767%   $178.4208   $178.42   $178.40   $178.40  
  7 purchase totals = $992.85       $1,099.5044   $1,099.51   $1,099.45   $1,099.50