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 $149.26   8.874%   $162.5053   $162.51   $162.50   $162.50  
  Purchase #2 $68.31   9.208%   $74.6   $74.60   $74.60   $74.60  
  Purchase #3 $242.61   4.781%   $254.2092   $254.21   $254.20   $254.20  
  Purchase #4 $198.47   13.824%   $225.9065   $225.91   $225.90   $225.90  
  Purchase #5 $200.42   7.432%   $215.3152   $215.32   $215.30   $215.30  
  Purchase #6 $82.77   4.523%   $86.5137   $86.51   $86.50   $86.50  
  Purchase #7 $204.44   5.146%   $214.9605   $214.96   $214.95   $215.00  
  7 purchase totals = $1,146.28       $1,234.0104   $1,234.02   $1,233.95   $1,234.00