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	$158.86	8.152%	$171.8103	$171.81	$171.80	$171.80
Purchase #2	$128.48	10.289%	$141.6993	$141.70	$141.70	$141.70
Purchase #3	$96.91	5.819%	$102.5492	$102.55	$102.55	$102.50
Purchase #4	$132.47	7.621%	$142.5655	$142.57	$142.55	$142.60
Purchase #5	$99.51	5.278%	$104.7621	$104.76	$104.75	$104.80
Purchase #6	$41.32	4.521%	$43.1881	$43.19	$43.20	$43.20
Purchase #7	$164.28	13.135%	$185.8582	$185.86	$185.85	$185.90
7 purchase totals =	$821.83		$892.4327	$892.44	$892.40	$892.50