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	$104.74	12.596%	$117.9331	$117.93	$117.95	$117.90
Purchase #2	$239.50	12.616%	$269.7153	$269.72	$269.70	$269.70
Purchase #3	$76.43	7.676%	$82.2968	$82.30	$82.30	$82.30
Purchase #4	$24.33	6.454%	$25.9003	$25.90	$25.90	$25.90
Purchase #5	$40.73	10.283%	$44.9183	$44.92	$44.90	$44.90
Purchase #6	$50.99	4.850%	$53.463	$53.46	$53.45	$53.50
Purchase #7	$123.58	3.548%	$127.9646	$127.96	$127.95	$128.00
7 purchase totals =	$660.30		$722.1914	$722.19	$722.15	$722.20