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	$123.54	6.290%	$131.3107	$131.31	$131.30	$131.30
Purchase #2	$239.78	7.779%	$258.4325	$258.43	$258.45	$258.40
Purchase #3	$216.71	6.556%	$230.9175	$230.92	$230.90	$230.90
Purchase #4	$106.71	5.539%	$112.6207	$112.62	$112.60	$112.60
Purchase #5	$58.70	11.470%	$65.4329	$65.43	$65.45	$65.40
Purchase #6	$17.33	4.646%	$18.1352	$18.14	$18.15	$18.10
Purchase #7	$200.66	7.603%	$215.9162	$215.92	$215.90	$215.90
7 purchase totals =	$963.43		$1,032.7657	$1,032.77	$1,032.75	$1,032.60