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	$47.28	5.137%	$49.7088	$49.71	$49.70	$49.70
Purchase #2	$143.52	5.822%	$151.8757	$151.88	$151.90	$151.90
Purchase #3	$107.31	10.472%	$118.5475	$118.55	$118.55	$118.50
Purchase #4	$131.97	13.842%	$150.2373	$150.24	$150.25	$150.20
Purchase #5	$155.38	8.538%	$168.6463	$168.65	$168.65	$168.60
Purchase #6	$179.89	9.269%	$196.564	$196.56	$196.55	$196.60
Purchase #7	$18.81	6.125%	$19.9621	$19.96	$19.95	$20.00
7 purchase totals =	$784.16		$855.5417	$855.55	$855.55	$855.50