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 $246.25   12.317%   $276.5806   $276.58   $276.60   $276.60  
  Purchase #2 $167.41   11.535%   $186.7207   $186.72   $186.70   $186.70  
  Purchase #3 $156.53   11.384%   $174.3494   $174.35   $174.35   $174.30  
  Purchase #4 $63.61   5.702%   $67.237   $67.24   $67.25   $67.20  
  Purchase #5 $29.61   3.797%   $30.7343   $30.73   $30.75   $30.70  
  Purchase #6 $188.25   13.417%   $213.5075   $213.51   $213.50   $213.50  
  Purchase #7 $245.91   5.664%   $259.8383   $259.84   $259.85   $259.80  
  7 purchase totals = $1,097.57       $1,208.9678   $1,208.97   $1,209.00   $1,208.80