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	$25.54	6.763%	$27.2673	$27.27	$27.25	$27.30
Purchase #2	$237.89	6.584%	$253.5527	$253.55	$253.55	$253.60
Purchase #3	$152.86	8.534%	$165.9051	$165.91	$165.90	$165.90
Purchase #4	$145.68	4.615%	$152.4031	$152.40	$152.40	$152.40
Purchase #5	$180.40	10.458%	$199.2662	$199.27	$199.25	$199.30
Purchase #6	$65.60	9.139%	$71.5952	$71.60	$71.60	$71.60
Purchase #7	$54.99	5.603%	$58.0711	$58.07	$58.05	$58.10
7 purchase totals =	$862.96		$928.0607	$928.07	$928.00	$928.20