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	$31.83	10.672%	$35.2269	$35.23	$35.25	$35.20
Purchase #2	$142.66	4.513%	$149.0982	$149.10	$149.10	$149.10
Purchase #3	$17.96	12.179%	$20.1473	$20.15	$20.15	$20.10
Purchase #4	$205.73	13.596%	$233.7011	$233.70	$233.70	$233.70
Purchase #5	$77.88	11.635%	$86.9413	$86.94	$86.95	$86.90
Purchase #6	$180.47	6.274%	$191.7927	$191.79	$191.80	$191.80
Purchase #7	$115.50	10.565%	$127.7026	$127.70	$127.70	$127.70
7 purchase totals =	$772.03		$844.6101	$844.61	$844.65	$844.50