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	$123.55	6.444%	$131.5116	$131.51	$131.50	$131.50
Purchase #2	$39.75	6.781%	$42.4454	$42.45	$42.45	$42.40
Purchase #3	$49.48	6.628%	$52.7595	$52.76	$52.75	$52.80
Purchase #4	$183.86	7.421%	$197.5043	$197.50	$197.50	$197.50
Purchase #5	$110.25	7.183%	$118.1693	$118.17	$118.15	$118.20
Purchase #6	$100.59	4.522%	$105.1387	$105.14	$105.15	$105.10
Purchase #7	$187.62	5.651%	$198.2224	$198.22	$198.20	$198.20
7 purchase totals =	$795.10		$845.7512	$845.75	$845.70	$845.70