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	$241.28	7.224%	$258.7101	$258.71	$258.70	$258.70
Purchase #2	$127.42	11.793%	$142.4466	$142.45	$142.45	$142.40
Purchase #3	$238.34	7.482%	$256.1726	$256.17	$256.15	$256.20
Purchase #4	$57.31	9.649%	$62.8398	$62.84	$62.85	$62.80
Purchase #5	$202.77	12.187%	$227.4816	$227.48	$227.50	$227.50
Purchase #6	$47.83	13.146%	$54.1177	$54.12	$54.10	$54.10
Purchase #7	$81.53	10.661%	$90.2219	$90.22	$90.20	$90.20
7 purchase totals =	$996.48		$1,091.9903	$1,091.99	$1,091.95	$1,091.90