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 $56.44   9.655%   $61.8893   $61.89   $61.90   $61.90  
  Purchase #2 $82.59   7.145%   $88.4911   $88.49   $88.50   $88.50  
  Purchase #3 $90.77   6.857%   $96.9941   $96.99   $97.00   $97.00  
  Purchase #4 $219.90   7.526%   $236.4497   $236.45   $236.45   $236.40  
  Purchase #5 $101.98   12.764%   $114.9967   $115.00   $115.00   $115.00  
  Purchase #6 $72.43   5.759%   $76.6012   $76.60   $76.60   $76.60  
  Purchase #7 $112.46   10.635%   $124.4201   $124.42   $124.40   $124.40  
  7 purchase totals = $736.57       $799.8422   $799.84   $799.85   $799.80