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	$173.25	3.471%	$179.2635	$179.26	$179.25	$179.30
Purchase #2	$58.48	9.652%	$64.1245	$64.12	$64.10	$64.10
Purchase #3	$199.52	5.133%	$209.7614	$209.76	$209.75	$209.80
Purchase #4	$177.52	3.622%	$183.9498	$183.95	$183.95	$183.90
Purchase #5	$85.61	5.444%	$90.2706	$90.27	$90.25	$90.30
Purchase #6	$37.67	13.198%	$42.6417	$42.64	$42.65	$42.60
Purchase #7	$191.72	9.493%	$209.92	$209.92	$209.90	$209.90
7 purchase totals =	$923.77		$979.9315	$979.92	$979.85	$979.90