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	$73.39	13.709%	$83.451	$83.45	$83.45	$83.50
Purchase #2	$118.99	4.749%	$124.6408	$124.64	$124.65	$124.60
Purchase #3	$134.71	5.176%	$141.6826	$141.68	$141.70	$141.70
Purchase #4	$162.43	6.467%	$172.9343	$172.93	$172.95	$172.90
Purchase #5	$37.41	4.572%	$39.1204	$39.12	$39.10	$39.10
Purchase #6	$123.73	12.326%	$138.981	$138.98	$139.00	$139.00
Purchase #7	$89.80	10.511%	$99.2389	$99.24	$99.25	$99.20
7 purchase totals =	$740.46		$800.0490	$800.04	$800.10	$800.00