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	$133.41	4.622%	$139.5762	$139.58	$139.60	$139.60
Purchase #2	$50.37	9.252%	$55.0302	$55.03	$55.05	$55.00
Purchase #3	$186.38	5.434%	$196.5079	$196.51	$196.50	$196.50
Purchase #4	$99.57	6.789%	$106.3298	$106.33	$106.35	$106.30
Purchase #5	$193.28	9.239%	$211.1371	$211.14	$211.15	$211.10
Purchase #6	$112.90	6.499%	$120.2374	$120.24	$120.25	$120.20
Purchase #7	$39.56	6.368%	$42.0792	$42.08	$42.10	$42.10
7 purchase totals =	$815.47		$870.8978	$870.91	$871.00	$870.80