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	$145.89	6.777%	$155.777	$155.78	$155.80	$155.80
Purchase #2	$132.58	7.749%	$142.8536	$142.85	$142.85	$142.90
Purchase #3	$192.37	6.439%	$204.7567	$204.76	$204.75	$204.80
Purchase #4	$146.68	9.746%	$160.9754	$160.98	$161.00	$161.00
Purchase #5	$25.56	12.636%	$28.7898	$28.79	$28.80	$28.80
Purchase #6	$190.93	10.779%	$211.5103	$211.51	$211.50	$211.50
Purchase #7	$92.51	6.434%	$98.4621	$98.46	$98.45	$98.50
7 purchase totals =	$926.52		$1,003.1249	$1,003.13	$1,003.15	$1,003.30