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	$35.56	9.801%	$39.0452	$39.05	$39.05	$39.00
Purchase #2	$222.52	10.344%	$245.5375	$245.54	$245.55	$245.50
Purchase #3	$142.37	7.451%	$152.978	$152.98	$153.00	$153.00
Purchase #4	$87.57	4.675%	$91.6639	$91.66	$91.65	$91.70
Purchase #5	$236.92	7.625%	$254.9852	$254.99	$255.00	$255.00
Purchase #6	$140.86	4.312%	$146.9339	$146.93	$146.95	$146.90
Purchase #7	$136.49	5.588%	$144.1171	$144.12	$144.10	$144.10
7 purchase totals =	$1,002.29		$1,075.2608	$1,075.27	$1,075.30	$1,075.20