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	$67.38	9.270%	$73.6261	$73.63	$73.65	$73.60
Purchase #2	$17.89	6.852%	$19.1158	$19.12	$19.10	$19.10
Purchase #3	$241.57	13.157%	$273.3534	$273.35	$273.35	$273.40
Purchase #4	$140.76	3.111%	$145.139	$145.14	$145.15	$145.10
Purchase #5	$160.31	12.194%	$179.8582	$179.86	$179.85	$179.90
Purchase #6	$119.75	7.356%	$128.5588	$128.56	$128.55	$128.60
Purchase #7	$92.64	13.141%	$104.8138	$104.81	$104.80	$104.80
7 purchase totals =	$840.30		$924.4651	$924.47	$924.45	$924.50