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	$75.61	6.187%	$80.288	$80.29	$80.30	$80.30
Purchase #2	$12.59	3.519%	$13.033	$13.03	$13.05	$13.00
Purchase #3	$185.52	9.572%	$203.278	$203.28	$203.30	$203.30
Purchase #4	$247.32	9.742%	$271.4139	$271.41	$271.40	$271.40
Purchase #5	$207.49	3.753%	$215.2771	$215.28	$215.30	$215.30
Purchase #6	$87.69	3.238%	$90.5294	$90.53	$90.55	$90.50
Purchase #7	$164.29	10.736%	$181.9282	$181.93	$181.95	$181.90
7 purchase totals =	$980.51		$1,055.7476	$1,055.75	$1,055.85	$1,055.70