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	$54.28	6.178%	$57.6334	$57.63	$57.65	$57.60
Purchase #2	$99.72	5.559%	$105.2634	$105.26	$105.25	$105.30
Purchase #3	$95.46	7.822%	$102.9269	$102.93	$102.95	$102.90
Purchase #4	$223.70	8.569%	$242.8689	$242.87	$242.85	$242.90
Purchase #5	$169.40	11.867%	$189.5027	$189.50	$189.50	$189.50
Purchase #6	$52.54	5.378%	$55.3656	$55.37	$55.35	$55.40
Purchase #7	$204.79	10.228%	$225.7359	$225.74	$225.75	$225.70
7 purchase totals =	$899.89		$979.2968	$979.30	$979.30	$979.30