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	$40.68	4.373%	$42.4589	$42.46	$42.45	$42.50
Purchase #2	$45.54	10.806%	$50.4611	$50.46	$50.45	$50.50
Purchase #3	$180.75	12.562%	$203.4558	$203.46	$203.45	$203.50
Purchase #4	$43.29	3.466%	$44.7904	$44.79	$44.80	$44.80
Purchase #5	$9.76	13.764%	$11.1034	$11.10	$11.10	$11.10
Purchase #6	$217.58	11.576%	$242.7671	$242.77	$242.75	$242.80
Purchase #7	$46.72	11.809%	$52.2372	$52.24	$52.25	$52.20
7 purchase totals =	$584.32		$647.2739	$647.28	$647.25	$647.40