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	$171.47	5.199%	$180.3847	$180.38	$180.40	$180.40
Purchase #2	$139.39	4.644%	$145.8633	$145.86	$145.85	$145.90
Purchase #3	$52.60	7.445%	$56.5161	$56.52	$56.50	$56.50
Purchase #4	$7.39	9.598%	$8.0993	$8.10	$8.10	$8.10
Purchase #5	$74.28	5.245%	$78.176	$78.18	$78.20	$78.20
Purchase #6	$166.83	11.699%	$186.3474	$186.35	$186.35	$186.30
Purchase #7	$212.50	3.260%	$219.4275	$219.43	$219.45	$219.40
7 purchase totals =	$824.46		$874.8143	$874.82	$874.85	$874.80