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	$155.54	8.180%	$168.2632	$168.26	$168.25	$168.30
Purchase #2	$196.54	9.451%	$215.115	$215.12	$215.10	$215.10
Purchase #3	$80.52	11.109%	$89.465	$89.47	$89.45	$89.50
Purchase #4	$30.55	5.279%	$32.1627	$32.16	$32.15	$32.20
Purchase #5	$26.88	12.159%	$30.1483	$30.15	$30.15	$30.10
Purchase #6	$90.43	5.613%	$95.5058	$95.51	$95.50	$95.50
Purchase #7	$239.50	7.795%	$258.169	$258.17	$258.15	$258.20
7 purchase totals =	$819.96		$888.8290	$888.84	$888.75	$888.90