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	$37.46	12.401%	$42.1054	$42.11	$42.10	$42.10
Purchase #2	$31.25	3.315%	$32.2859	$32.29	$32.30	$32.30
Purchase #3	$235.89	5.801%	$249.574	$249.57	$249.55	$249.60
Purchase #4	$46.75	5.521%	$49.3311	$49.33	$49.35	$49.30
Purchase #5	$230.57	10.429%	$254.6161	$254.62	$254.60	$254.60
Purchase #6	$224.42	7.172%	$240.5154	$240.52	$240.50	$240.50
Purchase #7	$206.28	9.736%	$226.3634	$226.36	$226.35	$226.40
7 purchase totals =	$1,012.62		$1,094.7913	$1,094.80	$1,094.75	$1,094.80