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	$52.82	7.720%	$56.8977	$56.90	$56.90	$56.90
Purchase #2	$84.40	5.770%	$89.2699	$89.27	$89.25	$89.30
Purchase #3	$143.91	7.166%	$154.2226	$154.22	$154.20	$154.20
Purchase #4	$163.66	11.393%	$182.3058	$182.31	$182.30	$182.30
Purchase #5	$244.51	6.783%	$261.0951	$261.10	$261.10	$261.10
Purchase #6	$34.53	7.645%	$37.1698	$37.17	$37.15	$37.20
Purchase #7	$49.90	7.259%	$53.5222	$53.52	$53.50	$53.50
7 purchase totals =	$773.73		$834.4831	$834.49	$834.40	$834.50