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	$45.28	12.305%	$50.8517	$50.85	$50.85	$50.90
Purchase #2	$120.49	9.209%	$131.5859	$131.59	$131.60	$131.60
Purchase #3	$216.46	12.645%	$243.8314	$243.83	$243.85	$243.80
Purchase #4	$230.62	13.676%	$262.1596	$262.16	$262.15	$262.20
Purchase #5	$57.76	8.871%	$62.8839	$62.88	$62.90	$62.90
Purchase #6	$145.41	3.636%	$150.6971	$150.70	$150.70	$150.70
Purchase #7	$99.86	8.582%	$108.43	$108.43	$108.45	$108.40
7 purchase totals =	$915.88		$1,010.4396	$1,010.44	$1,010.50	$1,010.50