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	$13.52	4.104%	$14.0749	$14.07	$14.05	$14.10
Purchase #2	$126.59	10.507%	$139.8908	$139.89	$139.90	$139.90
Purchase #3	$228.78	4.543%	$239.1735	$239.17	$239.15	$239.20
Purchase #4	$224.71	8.199%	$243.134	$243.13	$243.15	$243.10
Purchase #5	$79.39	5.593%	$83.8303	$83.83	$83.85	$83.80
Purchase #6	$49.57	4.558%	$51.8294	$51.83	$51.85	$51.80
Purchase #7	$54.82	11.680%	$61.223	$61.22	$61.20	$61.20
7 purchase totals =	$777.38		$833.1559	$833.14	$833.15	$833.10