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	$170.48	10.641%	$188.6208	$188.62	$188.60	$188.60
Purchase #2	$59.52	3.601%	$61.6633	$61.66	$61.65	$61.70
Purchase #3	$61.96	11.408%	$69.0284	$69.03	$69.05	$69.00
Purchase #4	$18.25	4.126%	$19.003	$19.00	$19.00	$19.00
Purchase #5	$172.62	13.831%	$196.4951	$196.50	$196.50	$196.50
Purchase #6	$203.55	13.678%	$231.3916	$231.39	$231.40	$231.40
Purchase #7	$134.67	13.406%	$152.7239	$152.72	$152.70	$152.70
7 purchase totals =	$821.05		$918.9261	$918.92	$918.90	$918.90