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	$107.94	6.340%	$114.7834	$114.78	$114.80	$114.80
Purchase #2	$92.84	11.836%	$103.8285	$103.83	$103.85	$103.80
Purchase #3	$211.74	5.149%	$222.6425	$222.64	$222.65	$222.60
Purchase #4	$134.33	9.413%	$146.9745	$146.97	$146.95	$147.00
Purchase #5	$27.70	4.717%	$29.0066	$29.01	$29.00	$29.00
Purchase #6	$188.78	6.396%	$200.8544	$200.85	$200.85	$200.90
Purchase #7	$242.32	10.850%	$268.6117	$268.61	$268.60	$268.60
7 purchase totals =	$1,005.65		$1,086.7016	$1,086.69	$1,086.70	$1,086.70