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	$165.87	7.666%	$178.5856	$178.59	$178.60	$178.60
Purchase #2	$38.39	11.855%	$42.9411	$42.94	$42.95	$42.90
Purchase #3	$204.64	7.787%	$220.5753	$220.58	$220.60	$220.60
Purchase #4	$180.79	12.666%	$203.6889	$203.69	$203.70	$203.70
Purchase #5	$49.64	9.529%	$54.3702	$54.37	$54.35	$54.40
Purchase #6	$165.29	13.640%	$187.8356	$187.84	$187.85	$187.80
Purchase #7	$117.84	7.850%	$127.0904	$127.09	$127.10	$127.10
7 purchase totals =	$922.46		$1,015.0871	$1,015.10	$1,015.15	$1,015.10