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	$57.58	11.865%	$64.4119	$64.41	$64.40	$64.40
Purchase #2	$102.54	8.126%	$110.8724	$110.87	$110.85	$110.90
Purchase #3	$166.94	3.533%	$172.838	$172.84	$172.85	$172.80
Purchase #4	$59.99	12.542%	$67.5139	$67.51	$67.50	$67.50
Purchase #5	$183.92	4.141%	$191.5361	$191.54	$191.55	$191.50
Purchase #6	$186.29	11.665%	$208.0207	$208.02	$208.00	$208.00
Purchase #7	$147.49	10.241%	$162.5945	$162.59	$162.60	$162.60
7 purchase totals =	$904.75		$977.7875	$977.78	$977.75	$977.70