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	$240.60	10.288%	$265.3529	$265.35	$265.35	$265.40
Purchase #2	$222.66	8.680%	$241.9869	$241.99	$242.00	$242.00
Purchase #3	$27.81	10.820%	$30.819	$30.82	$30.80	$30.80
Purchase #4	$40.52	11.565%	$45.2061	$45.21	$45.20	$45.20
Purchase #5	$113.33	12.280%	$127.2469	$127.25	$127.25	$127.20
Purchase #6	$89.82	7.829%	$96.852	$96.85	$96.85	$96.90
Purchase #7	$136.86	4.363%	$142.8312	$142.83	$142.85	$142.80
7 purchase totals =	$871.60		$950.2950	$950.30	$950.30	$950.30