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	$249.41	12.106%	$279.6036	$279.60	$279.60	$279.60
Purchase #2	$31.64	3.458%	$32.7341	$32.73	$32.75	$32.70
Purchase #3	$122.25	5.380%	$128.8271	$128.83	$128.85	$128.80
Purchase #4	$218.66	12.464%	$245.9138	$245.91	$245.90	$245.90
Purchase #5	$226.83	11.661%	$253.2806	$253.28	$253.30	$253.30
Purchase #6	$84.34	7.130%	$90.3534	$90.35	$90.35	$90.40
Purchase #7	$85.80	6.798%	$91.6327	$91.63	$91.65	$91.60
7 purchase totals =	$1,018.93		$1,122.3453	$1,122.33	$1,122.40	$1,122.30