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	$121.61	4.750%	$127.3865	$127.39	$127.40	$127.40
Purchase #2	$234.52	13.350%	$265.8284	$265.83	$265.85	$265.80
Purchase #3	$142.27	3.168%	$146.7771	$146.78	$146.80	$146.80
Purchase #4	$112.83	6.274%	$119.909	$119.91	$119.90	$119.90
Purchase #5	$209.52	11.268%	$233.1287	$233.13	$233.15	$233.10
Purchase #6	$203.65	12.590%	$229.2895	$229.29	$229.30	$229.30
Purchase #7	$76.34	10.122%	$84.0671	$84.07	$84.05	$84.10
7 purchase totals =	$1,100.74		$1,206.3863	$1,206.40	$1,206.45	$1,206.40