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 $245.74   11.235%   $273.3489   $273.35   $273.35   $273.30  
  Purchase #2 $136.57   7.384%   $146.6543   $146.65   $146.65   $146.70  
  Purchase #3 $188.99   3.841%   $196.2491   $196.25   $196.25   $196.20  
  Purchase #4 $235.28   8.477%   $255.2247   $255.22   $255.20   $255.20  
  Purchase #5 $10.73   8.527%   $11.6449   $11.64   $11.65   $11.60  
  Purchase #6 $158.56   3.779%   $164.552   $164.55   $164.55   $164.60  
  Purchase #7 $71.80   10.338%   $79.2227   $79.22   $79.20   $79.20  
  7 purchase totals = $1,047.67       $1,126.8966   $1,126.88   $1,126.85   $1,126.80