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	$180.69	12.836%	$203.8834	$203.88	$203.90	$203.90
Purchase #2	$97.48	12.342%	$109.511	$109.51	$109.50	$109.50
Purchase #3	$93.86	13.696%	$106.7151	$106.72	$106.70	$106.70
Purchase #4	$115.55	10.255%	$127.3997	$127.40	$127.40	$127.40
Purchase #5	$159.49	4.758%	$167.0785	$167.08	$167.10	$167.10
Purchase #6	$79.51	3.338%	$82.164	$82.16	$82.15	$82.20
Purchase #7	$22.29	5.612%	$23.5409	$23.54	$23.55	$23.50
7 purchase totals =	$748.87		$820.2926	$820.29	$820.30	$820.30