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	$49.69	11.702%	$55.5047	$55.50	$55.50	$55.50
Purchase #2	$56.79	3.283%	$58.6544	$58.65	$58.65	$58.70
Purchase #3	$248.90	5.850%	$263.4607	$263.46	$263.45	$263.50
Purchase #4	$167.91	3.426%	$173.6626	$173.66	$173.65	$173.70
Purchase #5	$168.71	7.823%	$181.9082	$181.91	$181.90	$181.90
Purchase #6	$131.96	13.728%	$150.0755	$150.08	$150.10	$150.10
Purchase #7	$122.61	7.559%	$131.8781	$131.88	$131.90	$131.90
7 purchase totals =	$946.57		$1,015.1442	$1,015.14	$1,015.15	$1,015.30