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	$42.70	9.564%	$46.7838	$46.78	$46.80	$46.80
Purchase #2	$37.94	12.111%	$42.5349	$42.53	$42.55	$42.50
Purchase #3	$128.83	4.778%	$134.9855	$134.99	$135.00	$135.00
Purchase #4	$203.30	8.188%	$219.9462	$219.95	$219.95	$219.90
Purchase #5	$147.37	12.706%	$166.0948	$166.09	$166.10	$166.10
Purchase #6	$83.44	7.403%	$89.6171	$89.62	$89.60	$89.60
Purchase #7	$75.43	9.290%	$82.4374	$82.44	$82.45	$82.40
7 purchase totals =	$719.01		$782.3997	$782.40	$782.45	$782.30