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 $243.30   8.354%   $263.6253   $263.63   $263.65   $263.60  
  Purchase #2 $102.96   13.145%   $116.4941   $116.49   $116.50   $116.50  
  Purchase #3 $230.73   11.379%   $256.9848   $256.98   $257.00   $257.00  
  Purchase #4 $40.61   7.801%   $43.778   $43.78   $43.80   $43.80  
  Purchase #5 $101.81   13.112%   $115.1593   $115.16   $115.15   $115.20  
  Purchase #6 $140.76   11.329%   $156.7067   $156.71   $156.70   $156.70  
  Purchase #7 $68.40   7.330%   $73.4137   $73.41   $73.40   $73.40  
  7 purchase totals = $928.57       $1,026.1619   $1,026.16   $1,026.20   $1,026.20