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	$11.26	4.644%	$11.7829	$11.78	$11.80	$11.80
Purchase #2	$244.83	4.751%	$256.4619	$256.46	$256.45	$256.50
Purchase #3	$148.86	7.781%	$160.4428	$160.44	$160.45	$160.40
Purchase #4	$81.42	11.741%	$90.9795	$90.98	$91.00	$91.00
Purchase #5	$115.93	9.668%	$127.1381	$127.14	$127.15	$127.10
Purchase #6	$198.89	11.142%	$221.0503	$221.05	$221.05	$221.10
Purchase #7	$110.57	4.284%	$115.3068	$115.31	$115.30	$115.30
7 purchase totals =	$911.76		$983.1623	$983.16	$983.20	$983.20