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	$14.71	4.843%	$15.4224	$15.42	$15.40	$15.40
Purchase #2	$249.80	11.413%	$278.3097	$278.31	$278.30	$278.30
Purchase #3	$101.60	9.301%	$111.0498	$111.05	$111.05	$111.00
Purchase #4	$81.65	10.432%	$90.1677	$90.17	$90.15	$90.20
Purchase #5	$208.34	11.864%	$233.0575	$233.06	$233.05	$233.10
Purchase #6	$179.56	9.203%	$196.0849	$196.08	$196.10	$196.10
Purchase #7	$171.93	11.413%	$191.5524	$191.55	$191.55	$191.60
7 purchase totals =	$1,007.59		$1,115.6444	$1,115.64	$1,115.60	$1,115.70