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	$170.40	10.788%	$188.7828	$188.78	$188.80	$188.80
Purchase #2	$124.39	13.419%	$141.0819	$141.08	$141.10	$141.10
Purchase #3	$141.91	9.403%	$155.2538	$155.25	$155.25	$155.30
Purchase #4	$193.63	13.557%	$219.8804	$219.88	$219.90	$219.90
Purchase #5	$183.57	8.142%	$198.5163	$198.52	$198.50	$198.50
Purchase #6	$186.71	12.418%	$209.8956	$209.90	$209.90	$209.90
Purchase #7	$12.57	7.776%	$13.5474	$13.55	$13.55	$13.50
7 purchase totals =	$1,013.18		$1,126.9582	$1,126.96	$1,127.00	$1,127.00