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	$45.69	7.481%	$49.1081	$49.11	$49.10	$49.10
Purchase #2	$33.28	5.175%	$35.0022	$35.00	$35.00	$35.00
Purchase #3	$17.78	3.654%	$18.4297	$18.43	$18.45	$18.40
Purchase #4	$127.46	8.521%	$138.3209	$138.32	$138.30	$138.30
Purchase #5	$168.55	10.282%	$185.8803	$185.88	$185.90	$185.90
Purchase #6	$207.90	4.242%	$216.7191	$216.72	$216.70	$216.70
Purchase #7	$56.51	10.449%	$62.4147	$62.41	$62.40	$62.40
7 purchase totals =	$657.17		$705.8750	$705.87	$705.85	$705.80