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	$127.82	11.784%	$142.8823	$142.88	$142.90	$142.90
Purchase #2	$67.92	3.506%	$70.3013	$70.30	$70.30	$70.30
Purchase #3	$188.80	11.159%	$209.8682	$209.87	$209.85	$209.90
Purchase #4	$96.72	4.212%	$100.7938	$100.79	$100.80	$100.80
Purchase #5	$190.52	7.670%	$205.1329	$205.13	$205.15	$205.10
Purchase #6	$167.58	9.174%	$182.9538	$182.95	$182.95	$183.00
Purchase #7	$55.48	10.300%	$61.1944	$61.19	$61.20	$61.20
7 purchase totals =	$894.84		$973.1267	$973.11	$973.15	$973.20