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	$107.78	8.453%	$116.8906	$116.89	$116.90	$116.90
Purchase #2	$192.64	9.688%	$211.303	$211.30	$211.30	$211.30
Purchase #3	$123.27	13.760%	$140.232	$140.23	$140.25	$140.20
Purchase #4	$57.85	7.733%	$62.3235	$62.32	$62.30	$62.30
Purchase #5	$78.90	13.421%	$89.4892	$89.49	$89.50	$89.50
Purchase #6	$181.92	7.281%	$195.1656	$195.17	$195.15	$195.20
Purchase #7	$172.43	12.360%	$193.7423	$193.74	$193.75	$193.70
7 purchase totals =	$914.79		$1,009.1462	$1,009.14	$1,009.15	$1,009.10