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 $67.94   13.707%   $77.2525   $77.25   $77.25   $77.30  
  Purchase #2 $186.83   6.810%   $199.5531   $199.55   $199.55   $199.60  
  Purchase #3 $233.33   5.449%   $246.0442   $246.04   $246.05   $246.00  
  Purchase #4 $61.88   4.712%   $64.7958   $64.80   $64.80   $64.80  
  Purchase #5 $89.70   9.591%   $98.3031   $98.30   $98.30   $98.30  
  Purchase #6 $61.90   5.490%   $65.2983   $65.30   $65.30   $65.30  
  Purchase #7 $74.44   6.655%   $79.394   $79.39   $79.40   $79.40  
  7 purchase totals = $776.02       $830.6410   $830.63   $830.65   $830.70