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 $61.30   13.386%   $69.5056   $69.51   $69.50   $69.50  
  Purchase #2 $114.63   8.665%   $124.5627   $124.56   $124.55   $124.60  
  Purchase #3 $66.25   6.205%   $70.3608   $70.36   $70.35   $70.40  
  Purchase #4 $38.67   8.467%   $41.9442   $41.94   $41.95   $41.90  
  Purchase #5 $110.30   12.454%   $124.0368   $124.04   $124.05   $124.00  
  Purchase #6 $82.28   5.617%   $86.9017   $86.90   $86.90   $86.90  
  Purchase #7 $210.50   9.743%   $231.009   $231.01   $231.00   $231.00  
  7 purchase totals = $683.93       $748.3208   $748.32   $748.30   $748.30