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	$79.28	5.732%	$83.8243	$83.82	$83.80	$83.80
Purchase #2	$38.30	12.664%	$43.1503	$43.15	$43.15	$43.20
Purchase #3	$141.97	8.585%	$154.1581	$154.16	$154.15	$154.20
Purchase #4	$101.95	4.417%	$106.4531	$106.45	$106.45	$106.50
Purchase #5	$152.29	8.814%	$165.7128	$165.71	$165.70	$165.70
Purchase #6	$184.33	8.418%	$199.8469	$199.85	$199.85	$199.80
Purchase #7	$238.46	7.164%	$255.5433	$255.54	$255.55	$255.50
7 purchase totals =	$936.58		$1,008.6888	$1,008.68	$1,008.65	$1,008.70