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	$134.45	3.629%	$139.3292	$139.33	$139.35	$139.30
Purchase #2	$52.55	8.569%	$57.053	$57.05	$57.05	$57.10
Purchase #3	$144.74	8.419%	$156.9257	$156.93	$156.95	$156.90
Purchase #4	$156.98	7.560%	$168.8477	$168.85	$168.85	$168.80
Purchase #5	$7.61	12.852%	$8.588	$8.59	$8.60	$8.60
Purchase #6	$98.81	12.860%	$111.517	$111.52	$111.50	$111.50
Purchase #7	$70.33	12.596%	$79.1888	$79.19	$79.20	$79.20
7 purchase totals =	$665.47		$721.4494	$721.46	$721.50	$721.40