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 $20.91   13.373%   $23.7063   $23.71   $23.70   $23.70  
  Purchase #2 $196.86   4.315%   $205.3545   $205.35   $205.35   $205.40  
  Purchase #3 $54.49   13.567%   $61.8827   $61.88   $61.90   $61.90  
  Purchase #4 $169.28   12.362%   $190.2064   $190.21   $190.20   $190.20  
  Purchase #5 $5.62   12.514%   $6.3233   $6.32   $6.30   $6.30  
  Purchase #6 $202.54   6.208%   $215.1137   $215.11   $215.10   $215.10  
  Purchase #7 $114.29   7.574%   $122.9463   $122.95   $122.95   $122.90  
  7 purchase totals = $763.99       $825.5332   $825.53   $825.50   $825.50