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	$77.28	3.548%	$80.0219	$80.02	$80.00	$80.00
Purchase #2	$80.98	12.274%	$90.9195	$90.92	$90.90	$90.90
Purchase #3	$184.60	8.112%	$199.5748	$199.57	$199.55	$199.60
Purchase #4	$187.69	3.514%	$194.2854	$194.29	$194.30	$194.30
Purchase #5	$28.78	8.385%	$31.1932	$31.19	$31.20	$31.20
Purchase #6	$223.45	13.826%	$254.3442	$254.34	$254.35	$254.30
Purchase #7	$216.91	5.184%	$228.1546	$228.15	$228.15	$228.20
7 purchase totals =	$999.69		$1,078.4936	$1,078.48	$1,078.45	$1,078.50