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	$14.83	6.791%	$15.8371	$15.84	$15.85	$15.80
Purchase #2	$153.46	3.659%	$159.0751	$159.08	$159.10	$159.10
Purchase #3	$52.63	13.647%	$59.8124	$59.81	$59.80	$59.80
Purchase #4	$199.70	9.325%	$218.322	$218.32	$218.30	$218.30
Purchase #5	$137.38	6.581%	$146.421	$146.42	$146.40	$146.40
Purchase #6	$249.32	13.385%	$282.6915	$282.69	$282.70	$282.70
Purchase #7	$153.73	3.104%	$158.5018	$158.50	$158.50	$158.50
7 purchase totals =	$961.05		$1,040.6609	$1,040.66	$1,040.65	$1,040.60