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	$49.55	6.569%	$52.8049	$52.80	$52.80	$52.80
Purchase #2	$180.92	4.714%	$189.4486	$189.45	$189.45	$189.40
Purchase #3	$190.39	11.125%	$211.5709	$211.57	$211.55	$211.60
Purchase #4	$188.73	5.854%	$199.7783	$199.78	$199.80	$199.80
Purchase #5	$219.48	7.593%	$236.1451	$236.15	$236.15	$236.10
Purchase #6	$239.89	13.187%	$271.5243	$271.52	$271.50	$271.50
Purchase #7	$34.81	13.279%	$39.4324	$39.43	$39.45	$39.40
7 purchase totals =	$1,103.77		$1,200.7045	$1,200.70	$1,200.70	$1,200.60