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	$178.78	13.145%	$202.2806	$202.28	$202.30	$202.30
Purchase #2	$65.41	5.217%	$68.8224	$68.82	$68.80	$68.80
Purchase #3	$55.38	12.150%	$62.1087	$62.11	$62.10	$62.10
Purchase #4	$167.38	10.419%	$184.8193	$184.82	$184.80	$184.80
Purchase #5	$103.77	7.339%	$111.3857	$111.39	$111.40	$111.40
Purchase #6	$231.49	12.873%	$261.2897	$261.29	$261.30	$261.30
Purchase #7	$231.85	8.191%	$250.8408	$250.84	$250.85	$250.80
7 purchase totals =	$1,034.06		$1,141.5472	$1,141.55	$1,141.55	$1,141.50