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 $192.53   10.617%   $212.9709   $212.97   $212.95   $213.00  
  Purchase #2 $150.61   8.396%   $163.2552   $163.26   $163.25   $163.30  
  Purchase #3 $117.57   10.521%   $129.9395   $129.94   $129.95   $129.90  
  Purchase #4 $24.50   8.330%   $26.5409   $26.54   $26.55   $26.50  
  Purchase #5 $96.41   3.624%   $99.9039   $99.90   $99.90   $99.90  
  Purchase #6 $30.59   8.267%   $33.1189   $33.12   $33.10   $33.10  
  Purchase #7 $64.63   12.648%   $72.8044   $72.80   $72.80   $72.80  
  7 purchase totals = $676.84       $738.5337   $738.53   $738.50   $738.50