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	$115.56	4.142%	$120.3465	$120.35	$120.35	$120.30
Purchase #2	$141.61	5.323%	$149.1479	$149.15	$149.15	$149.10
Purchase #3	$85.58	5.623%	$90.3922	$90.39	$90.40	$90.40
Purchase #4	$18.49	10.745%	$20.4768	$20.48	$20.50	$20.50
Purchase #5	$168.75	9.792%	$185.274	$185.27	$185.25	$185.30
Purchase #6	$88.36	11.509%	$98.5294	$98.53	$98.55	$98.50
Purchase #7	$100.94	12.557%	$113.615	$113.62	$113.60	$113.60
7 purchase totals =	$719.29		$777.7818	$777.79	$777.80	$777.70