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	$101.77	10.355%	$112.3083	$112.31	$112.30	$112.30
Purchase #2	$192.89	12.645%	$217.2809	$217.28	$217.30	$217.30
Purchase #3	$58.58	9.136%	$63.9319	$63.93	$63.95	$63.90
Purchase #4	$239.89	10.169%	$264.2844	$264.28	$264.30	$264.30
Purchase #5	$95.34	10.261%	$105.1228	$105.12	$105.10	$105.10
Purchase #6	$100.49	11.727%	$112.2745	$112.27	$112.25	$112.30
Purchase #7	$97.50	7.469%	$104.7823	$104.78	$104.80	$104.80
7 purchase totals =	$886.46		$979.9851	$979.97	$980.00	$980.00