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	$65.51	12.760%	$73.8691	$73.87	$73.85	$73.90
Purchase #2	$147.27	3.442%	$152.339	$152.34	$152.35	$152.30
Purchase #3	$198.59	11.235%	$220.9016	$220.90	$220.90	$220.90
Purchase #4	$25.97	9.461%	$28.427	$28.43	$28.45	$28.40
Purchase #5	$9.79	8.139%	$10.5868	$10.59	$10.60	$10.60
Purchase #6	$59.83	13.194%	$67.724	$67.72	$67.70	$67.70
Purchase #7	$33.71	13.757%	$38.3475	$38.35	$38.35	$38.30
7 purchase totals =	$540.67		$592.1950	$592.20	$592.20	$592.10