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	$50.37	8.419%	$54.6107	$54.61	$54.60	$54.60
Purchase #2	$44.47	13.294%	$50.3818	$50.38	$50.40	$50.40
Purchase #3	$202.28	8.575%	$219.6255	$219.63	$219.65	$219.60
Purchase #4	$109.34	7.592%	$117.6411	$117.64	$117.65	$117.60
Purchase #5	$38.59	13.719%	$43.8842	$43.88	$43.90	$43.90
Purchase #6	$125.94	13.624%	$143.0981	$143.10	$143.10	$143.10
Purchase #7	$171.65	11.340%	$191.1151	$191.12	$191.10	$191.10
7 purchase totals =	$742.64		$820.3565	$820.36	$820.40	$820.30