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	$88.53	13.318%	$100.3204	$100.32	$100.30	$100.30
Purchase #2	$105.49	4.198%	$109.9185	$109.92	$109.90	$109.90
Purchase #3	$109.73	10.275%	$121.0048	$121.00	$121.00	$121.00
Purchase #4	$30.38	6.239%	$32.2754	$32.28	$32.30	$32.30
Purchase #5	$181.37	8.322%	$196.4636	$196.46	$196.45	$196.50
Purchase #6	$234.99	7.639%	$252.9409	$252.94	$252.95	$252.90
Purchase #7	$140.84	13.226%	$159.4675	$159.47	$159.45	$159.50
7 purchase totals =	$891.33		$972.3911	$972.39	$972.35	$972.40