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	$125.38	13.521%	$142.3326	$142.33	$142.35	$142.30
Purchase #2	$82.32	8.241%	$89.104	$89.10	$89.10	$89.10
Purchase #3	$104.98	5.457%	$110.7088	$110.71	$110.70	$110.70
Purchase #4	$130.35	10.117%	$143.5375	$143.54	$143.55	$143.50
Purchase #5	$161.69	5.648%	$170.8223	$170.82	$170.80	$170.80
Purchase #6	$115.43	12.304%	$129.6325	$129.63	$129.65	$129.60
Purchase #7	$105.52	6.387%	$112.2596	$112.26	$112.25	$112.30
7 purchase totals =	$825.67		$898.3973	$898.39	$898.40	$898.30