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	$27.71	12.518%	$31.1787	$31.18	$31.20	$31.20
Purchase #2	$162.47	11.644%	$181.388	$181.39	$181.40	$181.40
Purchase #3	$89.41	3.579%	$92.61	$92.61	$92.60	$92.60
Purchase #4	$113.76	13.646%	$129.2837	$129.28	$129.30	$129.30
Purchase #5	$196.90	13.331%	$223.1487	$223.15	$223.15	$223.10
Purchase #6	$152.32	13.276%	$172.542	$172.54	$172.55	$172.50
Purchase #7	$219.95	8.815%	$239.3386	$239.34	$239.35	$239.30
7 purchase totals =	$962.52		$1,069.4897	$1,069.49	$1,069.55	$1,069.40