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	$205.31	4.144%	$213.818	$213.82	$213.80	$213.80
Purchase #2	$90.45	12.195%	$101.4804	$101.48	$101.50	$101.50
Purchase #3	$35.71	10.815%	$39.572	$39.57	$39.55	$39.60
Purchase #4	$46.77	13.504%	$53.0858	$53.09	$53.10	$53.10
Purchase #5	$53.95	3.663%	$55.9262	$55.93	$55.95	$55.90
Purchase #6	$215.33	5.318%	$226.7812	$226.78	$226.80	$226.80
Purchase #7	$102.84	6.112%	$109.1256	$109.13	$109.15	$109.10
7 purchase totals =	$750.36		$799.7892	$799.80	$799.85	$799.80