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 $61.50   10.589%   $68.0122   $68.01   $68.00   $68.00  
  Purchase #2 $129.83   10.706%   $143.7296   $143.73   $143.75   $143.70  
  Purchase #3 $245.73   13.306%   $278.4268   $278.43   $278.45   $278.40  
  Purchase #4 $107.47   5.637%   $113.5281   $113.53   $113.55   $113.50  
  Purchase #5 $84.95   13.383%   $96.3189   $96.32   $96.30   $96.30  
  Purchase #6 $214.46   9.232%   $234.2589   $234.26   $234.25   $234.30  
  Purchase #7 $117.58   4.271%   $122.6018   $122.60   $122.60   $122.60  
  7 purchase totals = $961.52       $1,056.8763   $1,056.88   $1,056.90   $1,056.80