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	$150.43	10.510%	$166.2402	$166.24	$166.25	$166.20
Purchase #2	$19.65	4.278%	$20.4906	$20.49	$20.50	$20.50
Purchase #3	$128.76	12.378%	$144.6979	$144.70	$144.70	$144.70
Purchase #4	$90.68	5.209%	$95.4035	$95.40	$95.40	$95.40
Purchase #5	$240.63	12.315%	$270.2636	$270.26	$270.25	$270.30
Purchase #6	$34.52	7.627%	$37.1528	$37.15	$37.15	$37.20
Purchase #7	$46.96	13.164%	$53.1418	$53.14	$53.15	$53.10
7 purchase totals =	$711.63		$787.3904	$787.38	$787.40	$787.40