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	$243.71	6.132%	$258.6543	$258.65	$258.65	$258.70
Purchase #2	$128.74	12.284%	$144.5544	$144.55	$144.55	$144.60
Purchase #3	$48.48	5.234%	$51.0174	$51.02	$51.00	$51.00
Purchase #4	$177.73	10.364%	$196.1499	$196.15	$196.15	$196.10
Purchase #5	$38.76	4.720%	$40.5895	$40.59	$40.60	$40.60
Purchase #6	$49.25	3.519%	$50.9831	$50.98	$51.00	$51.00
Purchase #7	$34.97	7.460%	$37.5788	$37.58	$37.60	$37.60
7 purchase totals =	$721.64		$779.5274	$779.52	$779.55	$779.60