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	$46.44	8.651%	$50.4575	$50.46	$50.45	$50.50
Purchase #2	$67.48	11.770%	$75.4224	$75.42	$75.40	$75.40
Purchase #3	$40.29	7.553%	$43.3331	$43.33	$43.35	$43.30
Purchase #4	$240.73	7.718%	$259.3095	$259.31	$259.30	$259.30
Purchase #5	$238.87	5.144%	$251.1575	$251.16	$251.15	$251.20
Purchase #6	$172.62	13.695%	$196.2603	$196.26	$196.25	$196.30
Purchase #7	$59.49	5.307%	$62.6471	$62.65	$62.65	$62.60
7 purchase totals =	$865.92		$938.5874	$938.59	$938.55	$938.60