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	$218.70	4.729%	$229.0423	$229.04	$229.05	$229.00
Purchase #2	$146.96	12.599%	$165.4755	$165.48	$165.50	$165.50
Purchase #3	$37.32	13.260%	$42.2686	$42.27	$42.25	$42.30
Purchase #4	$90.79	8.836%	$98.8122	$98.81	$98.80	$98.80
Purchase #5	$111.71	9.245%	$122.0376	$122.04	$122.05	$122.00
Purchase #6	$74.37	5.367%	$78.3614	$78.36	$78.35	$78.40
Purchase #7	$33.40	9.299%	$36.5059	$36.51	$36.50	$36.50
7 purchase totals =	$713.25		$772.5035	$772.51	$772.50	$772.50