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	$221.90	12.345%	$249.2936	$249.29	$249.30	$249.30
Purchase #2	$192.51	6.108%	$204.2685	$204.27	$204.25	$204.30
Purchase #3	$31.52	4.360%	$32.8943	$32.89	$32.90	$32.90
Purchase #4	$96.83	13.603%	$110.0018	$110.00	$110.00	$110.00
Purchase #5	$131.68	5.587%	$139.037	$139.04	$139.05	$139.00
Purchase #6	$172.60	6.451%	$183.7344	$183.73	$183.75	$183.70
Purchase #7	$93.92	7.284%	$100.7611	$100.76	$100.75	$100.80
7 purchase totals =	$940.96		$1,019.9907	$1,019.98	$1,020.00	$1,020.00