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 $244.67   11.831%   $273.6169   $273.62   $273.60   $273.60  
  Purchase #2 $216.83   10.541%   $239.6861   $239.69   $239.70   $239.70  
  Purchase #3 $120.54   4.707%   $126.2138   $126.21   $126.20   $126.20  
  Purchase #4 $92.74   6.397%   $98.6726   $98.67   $98.65   $98.70  
  Purchase #5 $94.68   12.213%   $106.2433   $106.24   $106.25   $106.20  
  Purchase #6 $98.39   10.315%   $108.5389   $108.54   $108.55   $108.50  
  Purchase #7 $200.94   10.250%   $221.5364   $221.54   $221.55   $221.50  
  7 purchase totals = $1,068.79       $1,174.5080   $1,174.51   $1,174.50   $1,174.40