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	$209.84	5.843%	$222.101	$222.10	$222.10	$222.10
Purchase #2	$107.83	8.280%	$116.7583	$116.76	$116.75	$116.80
Purchase #3	$131.45	6.306%	$139.7392	$139.74	$139.75	$139.70
Purchase #4	$178.53	4.258%	$186.1318	$186.13	$186.15	$186.10
Purchase #5	$28.66	12.628%	$32.2792	$32.28	$32.30	$32.30
Purchase #6	$100.48	12.226%	$112.7647	$112.76	$112.75	$112.80
Purchase #7	$156.68	6.274%	$166.5101	$166.51	$166.50	$166.50
7 purchase totals =	$913.47		$976.2843	$976.28	$976.30	$976.30