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 $61.79   5.518%   $65.1996   $65.20   $65.20   $65.20  
  Purchase #2 $51.71   4.232%   $53.8984   $53.90   $53.90   $53.90  
  Purchase #3 $10.69   10.803%   $11.8448   $11.84   $11.85   $11.80  
  Purchase #4 $136.55   3.657%   $141.5436   $141.54   $141.55   $141.50  
  Purchase #5 $149.41   5.477%   $157.5932   $157.59   $157.60   $157.60  
  Purchase #6 $53.67   9.782%   $58.92   $58.92   $58.90   $58.90  
  Purchase #7 $248.71   7.360%   $267.0151   $267.02   $267.00   $267.00  
  7 purchase totals = $712.53       $756.0147   $756.01   $756.00   $755.90