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	$52.53	12.403%	$59.0453	$59.05	$59.05	$59.00
Purchase #2	$46.87	12.569%	$52.7611	$52.76	$52.75	$52.80
Purchase #3	$173.76	10.557%	$192.1038	$192.10	$192.10	$192.10
Purchase #4	$106.74	7.695%	$114.9536	$114.95	$114.95	$115.00
Purchase #5	$104.75	4.594%	$109.5622	$109.56	$109.55	$109.60
Purchase #6	$54.41	3.633%	$56.3867	$56.39	$56.40	$56.40
Purchase #7	$224.50	4.238%	$234.0143	$234.01	$234.00	$234.00
7 purchase totals =	$763.56		$818.8270	$818.82	$818.80	$818.90