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	$115.79	10.819%	$128.3173	$128.32	$128.30	$128.30
Purchase #2	$68.75	3.788%	$71.3543	$71.35	$71.35	$71.40
Purchase #3	$140.70	13.463%	$159.6424	$159.64	$159.65	$159.60
Purchase #4	$218.83	3.552%	$226.6028	$226.60	$226.60	$226.60
Purchase #5	$103.83	5.109%	$109.1347	$109.13	$109.15	$109.10
Purchase #6	$128.32	10.368%	$141.6242	$141.62	$141.60	$141.60
Purchase #7	$61.64	9.160%	$67.2862	$67.29	$67.30	$67.30
7 purchase totals =	$837.86		$903.9619	$903.95	$903.95	$903.90