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	$55.39	4.636%	$57.9579	$57.96	$57.95	$58.00
Purchase #2	$84.31	9.563%	$92.3726	$92.37	$92.35	$92.40
Purchase #3	$238.82	10.598%	$264.1301	$264.13	$264.15	$264.10
Purchase #4	$139.96	11.501%	$156.0568	$156.06	$156.05	$156.10
Purchase #5	$118.94	4.240%	$123.9831	$123.98	$124.00	$124.00
Purchase #6	$162.46	7.513%	$174.6656	$174.67	$174.65	$174.70
Purchase #7	$121.28	8.517%	$131.6094	$131.61	$131.60	$131.60
7 purchase totals =	$921.16		$1,000.7755	$1,000.78	$1,000.75	$1,000.90