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	$156.50	10.156%	$172.3941	$172.39	$172.40	$172.40
Purchase #2	$138.94	12.807%	$156.734	$156.73	$156.75	$156.70
Purchase #3	$158.86	11.873%	$177.7214	$177.72	$177.70	$177.70
Purchase #4	$79.25	11.231%	$88.1506	$88.15	$88.15	$88.20
Purchase #5	$137.26	10.847%	$152.1486	$152.15	$152.15	$152.10
Purchase #6	$101.93	3.142%	$105.1326	$105.13	$105.15	$105.10
Purchase #7	$79.56	8.418%	$86.2574	$86.26	$86.25	$86.30
7 purchase totals =	$852.30		$938.5387	$938.53	$938.55	$938.50