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 $168.72   13.244%   $191.0653   $191.07   $191.05   $191.10  
  Purchase #2 $41.59   3.162%   $42.9051   $42.91   $42.90   $42.90  
  Purchase #3 $57.81   9.174%   $63.1135   $63.11   $63.10   $63.10  
  Purchase #4 $192.57   11.469%   $214.6559   $214.66   $214.65   $214.70  
  Purchase #5 $98.82   8.791%   $107.5073   $107.51   $107.50   $107.50  
  Purchase #6 $54.73   5.413%   $57.6925   $57.69   $57.70   $57.70  
  Purchase #7 $80.57   6.739%   $85.9996   $86.00   $86.00   $86.00  
  7 purchase totals = $694.81       $762.9392   $762.95   $762.90   $763.00