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	$178.88	6.828%	$191.0939	$191.09	$191.10	$191.10
Purchase #2	$161.54	3.650%	$167.4362	$167.44	$167.45	$167.40
Purchase #3	$18.25	8.797%	$19.8555	$19.86	$19.85	$19.90
Purchase #4	$60.31	12.136%	$67.6292	$67.63	$67.65	$67.60
Purchase #5	$94.39	4.866%	$98.983	$98.98	$99.00	$99.00
Purchase #6	$49.38	6.136%	$52.41	$52.41	$52.40	$52.40
Purchase #7	$107.44	3.454%	$111.151	$111.15	$111.15	$111.20
7 purchase totals =	$670.19		$708.5588	$708.56	$708.60	$708.60