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	$103.85	4.292%	$108.3072	$108.31	$108.30	$108.30
Purchase #2	$100.47	11.362%	$111.8854	$111.89	$111.90	$111.90
Purchase #3	$119.54	4.696%	$125.1536	$125.15	$125.15	$125.20
Purchase #4	$167.47	13.667%	$190.3581	$190.36	$190.35	$190.40
Purchase #5	$171.54	12.472%	$192.9345	$192.93	$192.95	$192.90
Purchase #6	$73.84	4.512%	$77.1717	$77.17	$77.15	$77.20
Purchase #7	$51.56	9.430%	$56.4221	$56.42	$56.40	$56.40
7 purchase totals =	$788.27		$862.2326	$862.23	$862.20	$862.30