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	$39.48	8.562%	$42.8603	$42.86	$42.85	$42.90
Purchase #2	$117.97	7.205%	$126.4697	$126.47	$126.45	$126.50
Purchase #3	$58.92	12.739%	$66.4258	$66.43	$66.45	$66.40
Purchase #4	$139.76	5.475%	$147.4119	$147.41	$147.40	$147.40
Purchase #5	$133.96	4.170%	$139.5461	$139.55	$139.55	$139.50
Purchase #6	$174.94	6.827%	$186.8832	$186.88	$186.90	$186.90
Purchase #7	$229.44	12.836%	$258.8909	$258.89	$258.90	$258.90
7 purchase totals =	$894.47		$968.4879	$968.49	$968.50	$968.50