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	$245.56	4.500%	$256.6102	$256.61	$256.60	$256.60
Purchase #2	$84.72	10.626%	$93.7223	$93.72	$93.70	$93.70
Purchase #3	$153.50	13.453%	$174.1504	$174.15	$174.15	$174.20
Purchase #4	$107.74	8.775%	$117.1942	$117.19	$117.20	$117.20
Purchase #5	$187.43	6.740%	$200.0628	$200.06	$200.05	$200.10
Purchase #6	$39.42	3.482%	$40.7926	$40.79	$40.80	$40.80
Purchase #7	$197.34	10.616%	$218.2896	$218.29	$218.30	$218.30
7 purchase totals =	$1,015.71		$1,100.8221	$1,100.81	$1,100.80	$1,100.90