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	$245.88	13.521%	$279.1254	$279.13	$279.15	$279.10
Purchase #2	$81.49	4.785%	$85.3893	$85.39	$85.40	$85.40
Purchase #3	$151.88	5.122%	$159.6593	$159.66	$159.65	$159.70
Purchase #4	$75.66	10.174%	$83.3576	$83.36	$83.35	$83.40
Purchase #5	$193.30	13.573%	$219.5366	$219.54	$219.55	$219.50
Purchase #6	$110.73	12.102%	$124.1305	$124.13	$124.15	$124.10
Purchase #7	$43.72	4.154%	$45.5361	$45.54	$45.55	$45.50
7 purchase totals =	$902.66		$996.7348	$996.75	$996.80	$996.70