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	$73.48	6.457%	$78.2246	$78.22	$78.20	$78.20
Purchase #2	$90.27	7.119%	$96.6963	$96.70	$96.70	$96.70
Purchase #3	$243.95	5.218%	$256.6793	$256.68	$256.70	$256.70
Purchase #4	$149.66	6.419%	$159.2667	$159.27	$159.25	$159.30
Purchase #5	$192.36	6.789%	$205.4193	$205.42	$205.40	$205.40
Purchase #6	$203.30	9.740%	$223.1014	$223.10	$223.10	$223.10
Purchase #7	$132.27	8.434%	$143.4257	$143.43	$143.45	$143.40
7 purchase totals =	$1,085.29		$1,162.8133	$1,162.82	$1,162.80	$1,162.80