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	$248.39	4.104%	$258.5839	$258.58	$258.60	$258.60
Purchase #2	$18.90	9.299%	$20.6575	$20.66	$20.65	$20.70
Purchase #3	$183.88	6.780%	$196.3471	$196.35	$196.35	$196.30
Purchase #4	$210.30	6.317%	$223.5847	$223.58	$223.60	$223.60
Purchase #5	$129.38	3.789%	$134.2822	$134.28	$134.30	$134.30
Purchase #6	$234.74	3.196%	$242.2423	$242.24	$242.25	$242.20
Purchase #7	$173.61	9.597%	$190.2714	$190.27	$190.25	$190.30
7 purchase totals =	$1,199.20		$1,265.9691	$1,265.96	$1,266.00	$1,266.00