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	$244.83	6.171%	$259.9385	$259.94	$259.95	$259.90
Purchase #2	$237.52	3.248%	$245.2346	$245.23	$245.25	$245.20
Purchase #3	$99.79	7.306%	$107.0807	$107.08	$107.10	$107.10
Purchase #4	$184.78	6.359%	$196.5302	$196.53	$196.55	$196.50
Purchase #5	$108.54	8.812%	$118.1045	$118.10	$118.10	$118.10
Purchase #6	$220.29	13.865%	$250.8332	$250.83	$250.85	$250.80
Purchase #7	$47.72	12.575%	$53.7208	$53.72	$53.70	$53.70
7 purchase totals =	$1,143.47		$1,231.4425	$1,231.43	$1,231.50	$1,231.30