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	$208.82	8.209%	$225.962	$225.96	$225.95	$226.00
Purchase #2	$241.76	5.433%	$254.8948	$254.89	$254.90	$254.90
Purchase #3	$122.53	4.484%	$128.0242	$128.02	$128.00	$128.00
Purchase #4	$104.54	6.483%	$111.3173	$111.32	$111.30	$111.30
Purchase #5	$80.55	9.484%	$88.1894	$88.19	$88.20	$88.20
Purchase #6	$104.62	6.370%	$111.2843	$111.28	$111.30	$111.30
Purchase #7	$246.69	4.839%	$258.6273	$258.63	$258.65	$258.60
7 purchase totals =	$1,109.51		$1,178.2993	$1,178.29	$1,178.30	$1,178.30