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	$38.49	5.383%	$40.5619	$40.56	$40.55	$40.60
Purchase #2	$235.85	7.717%	$254.0505	$254.05	$254.05	$254.10
Purchase #3	$46.86	5.109%	$49.2541	$49.25	$49.25	$49.30
Purchase #4	$178.41	6.537%	$190.0727	$190.07	$190.05	$190.10
Purchase #5	$105.87	8.668%	$115.0468	$115.05	$115.05	$115.00
Purchase #6	$209.80	13.667%	$238.4734	$238.47	$238.45	$238.50
Purchase #7	$246.64	9.254%	$269.4641	$269.46	$269.45	$269.50
7 purchase totals =	$1,061.92		$1,156.9235	$1,156.91	$1,156.85	$1,157.10