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	$50.80	13.318%	$57.5655	$57.57	$57.55	$57.60
Purchase #2	$59.76	9.474%	$65.4217	$65.42	$65.40	$65.40
Purchase #3	$145.79	13.700%	$165.7632	$165.76	$165.75	$165.80
Purchase #4	$223.94	13.450%	$254.0599	$254.06	$254.05	$254.10
Purchase #5	$190.63	9.406%	$208.5607	$208.56	$208.55	$208.60
Purchase #6	$100.55	3.742%	$104.3126	$104.31	$104.30	$104.30
Purchase #7	$52.39	8.500%	$56.8432	$56.84	$56.85	$56.80
7 purchase totals =	$823.86		$912.5268	$912.52	$912.45	$912.60