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	$66.92	9.773%	$73.4601	$73.46	$73.45	$73.50
Purchase #2	$78.43	13.624%	$89.1153	$89.12	$89.10	$89.10
Purchase #3	$28.59	10.280%	$31.5291	$31.53	$31.55	$31.50
Purchase #4	$68.66	4.358%	$71.6522	$71.65	$71.65	$71.70
Purchase #5	$191.72	3.583%	$198.5893	$198.59	$198.60	$198.60
Purchase #6	$70.52	7.230%	$75.6186	$75.62	$75.60	$75.60
Purchase #7	$181.52	6.259%	$192.8813	$192.88	$192.90	$192.90
7 purchase totals =	$686.36		$732.8459	$732.85	$732.85	$732.90