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	$18.31	10.553%	$20.2423	$20.24	$20.25	$20.20
Purchase #2	$145.86	13.581%	$165.6692	$165.67	$165.65	$165.70
Purchase #3	$10.89	10.416%	$12.0243	$12.02	$12.00	$12.00
Purchase #4	$184.28	6.789%	$196.7908	$196.79	$196.80	$196.80
Purchase #5	$67.34	12.747%	$75.9238	$75.92	$75.90	$75.90
Purchase #6	$147.36	13.386%	$167.0856	$167.09	$167.10	$167.10
Purchase #7	$126.80	6.137%	$134.5817	$134.58	$134.60	$134.60
7 purchase totals =	$700.84		$772.3177	$772.31	$772.30	$772.30