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	$231.26	5.788%	$244.6453	$244.65	$244.65	$244.60
Purchase #2	$112.70	11.150%	$125.2661	$125.27	$125.25	$125.30
Purchase #3	$72.85	7.739%	$78.4879	$78.49	$78.50	$78.50
Purchase #4	$96.92	3.397%	$100.2124	$100.21	$100.20	$100.20
Purchase #5	$103.80	9.743%	$113.9132	$113.91	$113.90	$113.90
Purchase #6	$19.37	12.346%	$21.7614	$21.76	$21.75	$21.80
Purchase #7	$103.79	12.130%	$116.3797	$116.38	$116.40	$116.40
7 purchase totals =	$740.69		$800.6660	$800.67	$800.65	$800.70