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	$203.98	12.112%	$228.6861	$228.69	$228.70	$228.70
Purchase #2	$243.94	13.705%	$277.372	$277.37	$277.35	$277.40
Purchase #3	$5.81	11.261%	$6.4643	$6.46	$6.45	$6.50
Purchase #4	$158.78	10.741%	$175.8346	$175.83	$175.85	$175.80
Purchase #5	$142.69	5.827%	$151.0045	$151.00	$151.00	$151.00
Purchase #6	$71.65	3.376%	$74.0689	$74.07	$74.05	$74.10
Purchase #7	$86.96	4.479%	$90.8549	$90.85	$90.85	$90.90
7 purchase totals =	$913.81		$1,004.2853	$1,004.27	$1,004.25	$1,004.40