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 $60.92   4.836%   $63.8661   $63.87   $63.85   $63.90  
  Purchase #2 $208.94   13.269%   $236.6642   $236.66   $236.65   $236.70  
  Purchase #3 $75.83   11.291%   $84.392   $84.39   $84.40   $84.40  
  Purchase #4 $84.83   13.238%   $96.0598   $96.06   $96.05   $96.10  
  Purchase #5 $109.36   5.651%   $115.5399   $115.54   $115.55   $115.50  
  Purchase #6 $120.39   9.707%   $132.0763   $132.08   $132.10   $132.10  
  Purchase #7 $192.50   3.577%   $199.3857   $199.39   $199.40   $199.40  
  7 purchase totals = $852.77       $927.9840   $927.99   $928.00   $928.10