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	$238.76	8.233%	$258.4171	$258.42	$258.40	$258.40
Purchase #2	$6.36	6.583%	$6.7787	$6.78	$6.80	$6.80
Purchase #3	$200.58	11.503%	$223.6527	$223.65	$223.65	$223.70
Purchase #4	$148.98	9.111%	$162.5536	$162.55	$162.55	$162.60
Purchase #5	$143.69	10.161%	$158.2903	$158.29	$158.30	$158.30
Purchase #6	$38.93	12.346%	$43.7363	$43.74	$43.75	$43.70
Purchase #7	$224.79	13.752%	$255.7031	$255.70	$255.70	$255.70
7 purchase totals =	$1,002.09		$1,109.1318	$1,109.13	$1,109.15	$1,109.20