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	$20.84	5.243%	$21.9326	$21.93	$21.95	$21.90
Purchase #2	$220.42	3.697%	$228.5689	$228.57	$228.55	$228.60
Purchase #3	$180.57	3.842%	$187.5075	$187.51	$187.50	$187.50
Purchase #4	$82.40	12.654%	$92.8269	$92.83	$92.85	$92.80
Purchase #5	$157.91	9.643%	$173.1373	$173.14	$173.15	$173.10
Purchase #6	$89.85	12.706%	$101.2663	$101.27	$101.25	$101.30
Purchase #7	$37.61	5.637%	$39.7301	$39.73	$39.75	$39.70
7 purchase totals =	$789.60		$844.9696	$844.98	$845.00	$844.90