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	$105.53	5.543%	$111.3795	$111.38	$111.40	$111.40
Purchase #2	$79.68	3.599%	$82.5477	$82.55	$82.55	$82.50
Purchase #3	$181.91	6.610%	$193.9343	$193.93	$193.95	$193.90
Purchase #4	$194.26	10.503%	$214.6631	$214.66	$214.65	$214.70
Purchase #5	$36.31	11.692%	$40.5554	$40.56	$40.55	$40.60
Purchase #6	$82.27	7.819%	$88.7027	$88.70	$88.70	$88.70
Purchase #7	$174.44	6.417%	$185.6338	$185.63	$185.65	$185.60
7 purchase totals =	$854.40		$917.4165	$917.41	$917.45	$917.40