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	$35.69	12.152%	$40.027	$40.03	$40.05	$40.00
Purchase #2	$19.77	5.741%	$20.905	$20.91	$20.90	$20.90
Purchase #3	$146.68	3.812%	$152.2714	$152.27	$152.25	$152.30
Purchase #4	$65.95	12.548%	$74.2254	$74.23	$74.25	$74.20
Purchase #5	$123.30	4.130%	$128.3923	$128.39	$128.40	$128.40
Purchase #6	$16.91	9.200%	$18.4657	$18.47	$18.45	$18.50
Purchase #7	$98.73	10.517%	$109.1134	$109.11	$109.10	$109.10
7 purchase totals =	$507.03		$543.4002	$543.41	$543.40	$543.40