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	$128.59	6.725%	$137.2377	$137.24	$137.25	$137.20
Purchase #2	$183.41	4.262%	$191.2269	$191.23	$191.25	$191.20
Purchase #3	$151.44	7.397%	$162.642	$162.64	$162.65	$162.60
Purchase #4	$96.98	3.699%	$100.5673	$100.57	$100.55	$100.60
Purchase #5	$36.35	4.348%	$37.9305	$37.93	$37.95	$37.90
Purchase #6	$124.99	6.244%	$132.7944	$132.79	$132.80	$132.80
Purchase #7	$212.34	13.162%	$240.2882	$240.29	$240.30	$240.30
7 purchase totals =	$934.10		$1,002.6870	$1,002.69	$1,002.75	$1,002.60