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	$48.84	5.799%	$51.6722	$51.67	$51.65	$51.70
Purchase #2	$25.27	11.453%	$28.1642	$28.16	$28.15	$28.20
Purchase #3	$230.35	9.185%	$251.5076	$251.51	$251.50	$251.50
Purchase #4	$82.73	9.275%	$90.4032	$90.40	$90.40	$90.40
Purchase #5	$241.78	4.139%	$251.7873	$251.79	$251.80	$251.80
Purchase #6	$152.74	9.284%	$166.9204	$166.92	$166.90	$166.90
Purchase #7	$84.64	7.364%	$90.8729	$90.87	$90.85	$90.90
7 purchase totals =	$866.35		$931.3278	$931.32	$931.25	$931.40