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	$52.64	5.848%	$55.7184	$55.72	$55.70	$55.70
Purchase #2	$135.83	6.130%	$144.1564	$144.16	$144.15	$144.20
Purchase #3	$215.42	4.496%	$225.1053	$225.11	$225.10	$225.10
Purchase #4	$159.39	3.408%	$164.822	$164.82	$164.80	$164.80
Purchase #5	$133.38	6.790%	$142.4365	$142.44	$142.45	$142.40
Purchase #6	$136.57	13.469%	$154.9646	$154.96	$154.95	$155.00
Purchase #7	$173.46	9.555%	$190.0341	$190.03	$190.05	$190.00
7 purchase totals =	$1,006.69		$1,077.2373	$1,077.24	$1,077.20	$1,077.20