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	$122.89	8.627%	$133.4917	$133.49	$133.50	$133.50
Purchase #2	$139.46	9.386%	$152.5497	$152.55	$152.55	$152.50
Purchase #3	$123.69	5.176%	$130.0922	$130.09	$130.10	$130.10
Purchase #4	$225.89	13.846%	$257.1667	$257.17	$257.15	$257.20
Purchase #5	$10.73	8.380%	$11.6292	$11.63	$11.65	$11.60
Purchase #6	$25.42	12.128%	$28.5029	$28.50	$28.50	$28.50
Purchase #7	$115.49	7.317%	$123.9404	$123.94	$123.95	$123.90
7 purchase totals =	$763.57		$837.3728	$837.37	$837.40	$837.30