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	$39.52	9.122%	$43.125	$43.13	$43.15	$43.10
Purchase #2	$211.40	6.608%	$225.3693	$225.37	$225.35	$225.40
Purchase #3	$156.63	9.597%	$171.6618	$171.66	$171.65	$171.70
Purchase #4	$183.30	13.451%	$207.9557	$207.96	$207.95	$208.00
Purchase #5	$116.58	10.563%	$128.8943	$128.89	$128.90	$128.90
Purchase #6	$82.91	7.411%	$89.0545	$89.05	$89.05	$89.10
Purchase #7	$33.78	12.246%	$37.9167	$37.92	$37.90	$37.90
7 purchase totals =	$824.12		$903.9773	$903.98	$903.95	$904.10