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	$90.82	12.513%	$102.1843	$102.18	$102.20	$102.20
Purchase #2	$158.51	9.255%	$173.1801	$173.18	$173.20	$173.20
Purchase #3	$54.37	8.445%	$58.9615	$58.96	$58.95	$59.00
Purchase #4	$169.81	9.139%	$185.3289	$185.33	$185.35	$185.30
Purchase #5	$16.80	10.156%	$18.5062	$18.51	$18.50	$18.50
Purchase #6	$226.42	10.104%	$249.2975	$249.30	$249.30	$249.30
Purchase #7	$128.91	10.527%	$142.4804	$142.48	$142.50	$142.50
7 purchase totals =	$845.64		$929.9389	$929.94	$930.00	$930.00