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	$247.71	3.713%	$256.9075	$256.91	$256.90	$256.90
Purchase #2	$136.74	7.368%	$146.815	$146.82	$146.80	$146.80
Purchase #3	$96.78	3.754%	$100.4131	$100.41	$100.40	$100.40
Purchase #4	$231.39	13.659%	$262.9956	$263.00	$263.00	$263.00
Purchase #5	$123.97	12.191%	$139.0832	$139.08	$139.10	$139.10
Purchase #6	$182.75	12.426%	$205.4585	$205.46	$205.45	$205.50
Purchase #7	$235.94	12.372%	$265.1305	$265.13	$265.15	$265.10
7 purchase totals =	$1,255.28		$1,376.8034	$1,376.81	$1,376.80	$1,376.80