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	$78.62	7.239%	$84.3113	$84.31	$84.30	$84.30
Purchase #2	$139.39	12.497%	$156.8096	$156.81	$156.80	$156.80
Purchase #3	$130.91	8.532%	$142.0792	$142.08	$142.10	$142.10
Purchase #4	$184.91	12.595%	$208.1994	$208.20	$208.20	$208.20
Purchase #5	$156.99	6.327%	$166.9228	$166.92	$166.90	$166.90
Purchase #6	$121.55	4.736%	$127.3066	$127.31	$127.30	$127.30
Purchase #7	$83.52	11.745%	$93.3294	$93.33	$93.35	$93.30
7 purchase totals =	$895.89		$978.9583	$978.96	$978.95	$978.90