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	$5.76	12.669%	$6.4897	$6.49	$6.50	$6.50
Purchase #2	$167.75	3.701%	$173.9584	$173.96	$173.95	$174.00
Purchase #3	$73.25	7.287%	$78.5877	$78.59	$78.60	$78.60
Purchase #4	$158.82	4.839%	$166.5053	$166.51	$166.50	$166.50
Purchase #5	$196.71	6.504%	$209.504	$209.50	$209.50	$209.50
Purchase #6	$56.78	4.462%	$59.3135	$59.31	$59.30	$59.30
Purchase #7	$145.60	3.307%	$150.415	$150.42	$150.40	$150.40
7 purchase totals =	$804.67		$844.7736	$844.78	$844.75	$844.80