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	$239.99	12.430%	$269.8208	$269.82	$269.80	$269.80
Purchase #2	$55.73	12.740%	$62.83	$62.83	$62.85	$62.80
Purchase #3	$124.56	5.855%	$131.853	$131.85	$131.85	$131.90
Purchase #4	$26.34	9.125%	$28.7435	$28.74	$28.75	$28.70
Purchase #5	$76.52	7.246%	$82.0646	$82.06	$82.05	$82.10
Purchase #6	$208.45	8.796%	$226.7853	$226.79	$226.80	$226.80
Purchase #7	$159.75	4.824%	$167.4563	$167.46	$167.45	$167.50
7 purchase totals =	$891.34		$969.5535	$969.55	$969.55	$969.60