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	$125.82	4.236%	$131.1497	$131.15	$131.15	$131.10
Purchase #2	$142.98	9.538%	$156.6174	$156.62	$156.60	$156.60
Purchase #3	$106.98	3.563%	$110.7917	$110.79	$110.80	$110.80
Purchase #4	$123.80	3.653%	$128.3224	$128.32	$128.30	$128.30
Purchase #5	$168.67	13.603%	$191.6142	$191.61	$191.60	$191.60
Purchase #6	$88.58	5.435%	$93.3943	$93.39	$93.40	$93.40
Purchase #7	$107.61	3.408%	$111.2773	$111.28	$111.30	$111.30
7 purchase totals =	$864.44		$923.1670	$923.16	$923.15	$923.10