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	$11.70	6.188%	$12.424	$12.42	$12.40	$12.40
Purchase #2	$226.76	12.469%	$255.0347	$255.03	$255.05	$255.00
Purchase #3	$70.29	13.160%	$79.5402	$79.54	$79.55	$79.50
Purchase #4	$216.71	11.363%	$241.3348	$241.33	$241.35	$241.30
Purchase #5	$174.66	12.454%	$196.4122	$196.41	$196.40	$196.40
Purchase #6	$185.36	11.662%	$206.9767	$206.98	$207.00	$207.00
Purchase #7	$166.98	8.574%	$181.2969	$181.30	$181.30	$181.30
7 purchase totals =	$1,052.46		$1,173.0195	$1,173.01	$1,173.05	$1,172.90