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	$123.32	10.581%	$136.3685	$136.37	$136.35	$136.40
Purchase #2	$21.88	13.187%	$24.7653	$24.77	$24.75	$24.80
Purchase #3	$31.52	5.698%	$33.316	$33.32	$33.30	$33.30
Purchase #4	$233.72	6.596%	$249.1362	$249.14	$249.15	$249.10
Purchase #5	$222.35	8.764%	$241.8368	$241.84	$241.85	$241.80
Purchase #6	$113.77	11.832%	$127.2313	$127.23	$127.25	$127.20
Purchase #7	$206.49	9.848%	$226.8251	$226.83	$226.85	$226.80
7 purchase totals =	$953.05		$1,039.4792	$1,039.50	$1,039.50	$1,039.40