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	$166.84	3.371%	$172.4642	$172.46	$172.45	$172.50
Purchase #2	$109.74	8.574%	$119.1491	$119.15	$119.15	$119.10
Purchase #3	$158.81	9.741%	$174.2797	$174.28	$174.30	$174.30
Purchase #4	$172.92	4.157%	$180.1083	$180.11	$180.10	$180.10
Purchase #5	$94.40	6.215%	$100.267	$100.27	$100.25	$100.30
Purchase #6	$41.60	4.264%	$43.3738	$43.37	$43.35	$43.40
Purchase #7	$27.65	7.118%	$29.6181	$29.62	$29.60	$29.60
7 purchase totals =	$771.96		$819.2602	$819.26	$819.20	$819.30