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	$210.41	9.332%	$230.0455	$230.05	$230.05	$230.00
Purchase #2	$238.39	6.760%	$254.5052	$254.51	$254.50	$254.50
Purchase #3	$193.70	11.472%	$215.9213	$215.92	$215.90	$215.90
Purchase #4	$63.90	10.274%	$70.4651	$70.47	$70.45	$70.50
Purchase #5	$36.63	6.157%	$38.8853	$38.89	$38.90	$38.90
Purchase #6	$38.63	3.623%	$40.0296	$40.03	$40.05	$40.00
Purchase #7	$151.76	9.328%	$165.9162	$165.92	$165.90	$165.90
7 purchase totals =	$933.42		$1,015.7682	$1,015.79	$1,015.75	$1,015.70