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	$164.93	12.378%	$185.345	$185.35	$185.35	$185.30
Purchase #2	$214.41	4.329%	$223.6918	$223.69	$223.70	$223.70
Purchase #3	$78.98	7.647%	$85.0196	$85.02	$85.00	$85.00
Purchase #4	$77.38	4.324%	$80.7259	$80.73	$80.75	$80.70
Purchase #5	$173.89	9.490%	$190.3922	$190.39	$190.40	$190.40
Purchase #6	$12.88	9.763%	$14.1375	$14.14	$14.15	$14.10
Purchase #7	$61.81	12.332%	$69.4324	$69.43	$69.45	$69.40
7 purchase totals =	$784.28		$848.7444	$848.75	$848.80	$848.60