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 $188.53   13.466%   $213.9174   $213.92   $213.90   $213.90  
  Purchase #2 $90.39   5.753%   $95.5901   $95.59   $95.60   $95.60  
  Purchase #3 $54.54   7.552%   $58.6589   $58.66   $58.65   $58.70  
  Purchase #4 $163.94   12.414%   $184.2915   $184.29   $184.30   $184.30  
  Purchase #5 $242.29   8.246%   $262.2692   $262.27   $262.25   $262.30  
  Purchase #6 $45.92   11.179%   $51.0534   $51.05   $51.05   $51.10  
  Purchase #7 $171.63   10.275%   $189.265   $189.27   $189.25   $189.30  
  7 purchase totals = $957.24       $1,055.0455   $1,055.05   $1,055.00   $1,055.20