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	$77.54	7.767%	$83.5625	$83.56	$83.55	$83.60
Purchase #2	$108.95	10.667%	$120.5717	$120.57	$120.55	$120.60
Purchase #3	$35.31	12.399%	$39.6881	$39.69	$39.70	$39.70
Purchase #4	$41.33	11.682%	$46.1582	$46.16	$46.15	$46.20
Purchase #5	$34.51	7.351%	$37.0468	$37.05	$37.05	$37.00
Purchase #6	$90.30	8.560%	$98.0297	$98.03	$98.05	$98.00
Purchase #7	$112.60	3.388%	$116.4149	$116.41	$116.40	$116.40
7 purchase totals =	$500.54		$541.4719	$541.47	$541.45	$541.50