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 $248.34   4.298%   $259.0137   $259.01   $259.00   $259.00  
  Purchase #2 $175.39   9.388%   $191.8556   $191.86   $191.85   $191.90  
  Purchase #3 $131.62   13.715%   $149.6717   $149.67   $149.65   $149.70  
  Purchase #4 $155.88   3.602%   $161.4948   $161.49   $161.50   $161.50  
  Purchase #5 $82.39   5.213%   $86.685   $86.69   $86.70   $86.70  
  Purchase #6 $243.40   4.527%   $254.4187   $254.42   $254.40   $254.40  
  Purchase #7 $23.41   4.563%   $24.4782   $24.48   $24.50   $24.50  
  7 purchase totals = $1,060.43       $1,127.6177   $1,127.62   $1,127.60   $1,127.70