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	$150.94	13.662%	$171.5614	$171.56	$171.55	$171.60
Purchase #2	$194.49	7.153%	$208.4019	$208.40	$208.40	$208.40
Purchase #3	$218.41	13.315%	$247.4913	$247.49	$247.50	$247.50
Purchase #4	$173.38	6.643%	$184.8976	$184.90	$184.90	$184.90
Purchase #5	$229.83	12.421%	$258.3772	$258.38	$258.40	$258.40
Purchase #6	$100.35	10.750%	$111.1376	$111.14	$111.15	$111.10
Purchase #7	$55.59	7.614%	$59.8226	$59.82	$59.80	$59.80
7 purchase totals =	$1,122.99		$1,241.6896	$1,241.69	$1,241.70	$1,241.70