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	$98.78	6.313%	$105.016	$105.02	$105.00	$105.00
Purchase #2	$88.78	13.152%	$100.4563	$100.46	$100.45	$100.50
Purchase #3	$76.99	4.252%	$80.2636	$80.26	$80.25	$80.30
Purchase #4	$53.71	5.214%	$56.5104	$56.51	$56.50	$56.50
Purchase #5	$162.84	10.303%	$179.6174	$179.62	$179.60	$179.60
Purchase #6	$239.89	3.847%	$249.1186	$249.12	$249.10	$249.10
Purchase #7	$136.44	8.180%	$147.6008	$147.60	$147.60	$147.60
7 purchase totals =	$857.43		$918.5831	$918.59	$918.50	$918.60