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	$158.83	7.389%	$170.5659	$170.57	$170.55	$170.60
Purchase #2	$191.98	9.514%	$210.245	$210.25	$210.25	$210.20
Purchase #3	$127.83	8.544%	$138.7518	$138.75	$138.75	$138.80
Purchase #4	$85.51	5.528%	$90.237	$90.24	$90.25	$90.20
Purchase #5	$77.69	13.194%	$87.9404	$87.94	$87.95	$87.90
Purchase #6	$153.40	13.592%	$174.2501	$174.25	$174.25	$174.30
Purchase #7	$25.43	13.555%	$28.877	$28.88	$28.90	$28.90
7 purchase totals =	$820.67		$900.8672	$900.88	$900.90	$900.90