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	$92.65	7.414%	$99.5191	$99.52	$99.50	$99.50
Purchase #2	$113.41	12.287%	$127.3447	$127.34	$127.35	$127.30
Purchase #3	$139.83	5.195%	$147.0942	$147.09	$147.10	$147.10
Purchase #4	$102.32	11.349%	$113.9323	$113.93	$113.95	$113.90
Purchase #5	$247.60	6.763%	$264.3452	$264.35	$264.35	$264.30
Purchase #6	$35.46	10.836%	$39.3024	$39.30	$39.30	$39.30
Purchase #7	$148.84	10.665%	$164.7138	$164.71	$164.70	$164.70
7 purchase totals =	$880.11		$956.2517	$956.24	$956.25	$956.10