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 $57.72   8.250%   $62.4819   $62.48   $62.50   $62.50  
  Purchase #2 $25.98   3.622%   $26.921   $26.92   $26.90   $26.90  
  Purchase #3 $119.84   6.704%   $127.8741   $127.87   $127.85   $127.90  
  Purchase #4 $164.27   5.584%   $173.4428   $173.44   $173.45   $173.40  
  Purchase #5 $203.83   7.637%   $219.3965   $219.40   $219.40   $219.40  
  Purchase #6 $18.66   8.594%   $20.2636   $20.26   $20.25   $20.30  
  Purchase #7 $129.26   6.430%   $137.5714   $137.57   $137.55   $137.60  
  7 purchase totals = $719.56       $767.9513   $767.94   $767.90   $768.00