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 $64.80   6.474%   $68.9952   $69.00   $69.00   $69.00  
  Purchase #2 $242.87   13.573%   $275.8347   $275.83   $275.85   $275.80  
  Purchase #3 $93.37   12.665%   $105.1953   $105.20   $105.20   $105.20  
  Purchase #4 $60.61   5.160%   $63.7375   $63.74   $63.75   $63.70  
  Purchase #5 $122.46   8.243%   $132.5544   $132.55   $132.55   $132.60  
  Purchase #6 $212.42   11.316%   $236.4574   $236.46   $236.45   $236.50  
  Purchase #7 $169.97   12.325%   $190.9188   $190.92   $190.90   $190.90  
  7 purchase totals = $966.50       $1,073.6933   $1,073.70   $1,073.70   $1,073.70