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	$51.31	10.588%	$56.7427	$56.74	$56.75	$56.70
Purchase #2	$53.49	7.586%	$57.5478	$57.55	$57.55	$57.50
Purchase #3	$166.58	7.830%	$179.6232	$179.62	$179.60	$179.60
Purchase #4	$41.63	4.499%	$43.5029	$43.50	$43.50	$43.50
Purchase #5	$165.90	9.639%	$181.8911	$181.89	$181.90	$181.90
Purchase #6	$96.97	8.772%	$105.4762	$105.48	$105.50	$105.50
Purchase #7	$233.49	11.140%	$259.5008	$259.50	$259.50	$259.50
7 purchase totals =	$809.37		$884.2847	$884.28	$884.30	$884.20