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	$108.35	3.124%	$111.7349	$111.73	$111.75	$111.70
Purchase #2	$142.25	5.330%	$149.8319	$149.83	$149.85	$149.80
Purchase #3	$99.67	4.618%	$104.2728	$104.27	$104.25	$104.30
Purchase #4	$114.77	12.281%	$128.8649	$128.86	$128.85	$128.90
Purchase #5	$219.39	5.581%	$231.6342	$231.63	$231.65	$231.60
Purchase #6	$40.64	10.459%	$44.8905	$44.89	$44.90	$44.90
Purchase #7	$51.52	5.718%	$54.4659	$54.47	$54.45	$54.50
7 purchase totals =	$776.59		$825.6951	$825.68	$825.70	$825.70