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	$131.44	5.794%	$139.0556	$139.06	$139.05	$139.10
Purchase #2	$198.30	6.559%	$211.3065	$211.31	$211.30	$211.30
Purchase #3	$10.62	13.232%	$12.0252	$12.03	$12.05	$12.00
Purchase #4	$150.34	10.520%	$166.1558	$166.16	$166.15	$166.20
Purchase #5	$142.96	9.451%	$156.4711	$156.47	$156.45	$156.50
Purchase #6	$133.40	13.365%	$151.2289	$151.23	$151.25	$151.20
Purchase #7	$36.41	8.502%	$39.5056	$39.51	$39.50	$39.50
7 purchase totals =	$803.47		$875.7487	$875.77	$875.75	$875.80