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	$120.44	3.698%	$124.8939	$124.89	$124.90	$124.90
Purchase #2	$169.81	8.683%	$184.5546	$184.55	$184.55	$184.60
Purchase #3	$220.61	6.469%	$234.8813	$234.88	$234.90	$234.90
Purchase #4	$52.56	6.775%	$56.1209	$56.12	$56.10	$56.10
Purchase #5	$250.84	12.478%	$282.1398	$282.14	$282.15	$282.10
Purchase #6	$11.64	5.530%	$12.2837	$12.28	$12.30	$12.30
Purchase #7	$225.29	13.335%	$255.3324	$255.33	$255.35	$255.30
7 purchase totals =	$1,051.19		$1,150.2066	$1,150.19	$1,150.25	$1,150.20