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	$47.48	12.163%	$53.255	$53.26	$53.25	$53.30
Purchase #2	$155.25	11.800%	$173.5695	$173.57	$173.55	$173.60
Purchase #3	$97.27	4.265%	$101.4186	$101.42	$101.40	$101.40
Purchase #4	$67.31	8.316%	$72.9075	$72.91	$72.90	$72.90
Purchase #5	$86.94	9.624%	$95.3071	$95.31	$95.30	$95.30
Purchase #6	$117.54	10.452%	$129.8253	$129.83	$129.85	$129.80
Purchase #7	$35.72	9.581%	$39.1423	$39.14	$39.15	$39.10
7 purchase totals =	$607.51		$665.4253	$665.44	$665.40	$665.40