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	$38.85	4.561%	$40.6219	$40.62	$40.60	$40.60
Purchase #2	$148.73	3.864%	$154.4769	$154.48	$154.50	$154.50
Purchase #3	$38.83	7.182%	$41.6188	$41.62	$41.60	$41.60
Purchase #4	$64.91	11.102%	$72.1163	$72.12	$72.10	$72.10
Purchase #5	$183.79	4.267%	$191.6323	$191.63	$191.65	$191.60
Purchase #6	$37.93	9.351%	$41.4768	$41.48	$41.50	$41.50
Purchase #7	$224.28	5.403%	$236.3978	$236.40	$236.40	$236.40
7 purchase totals =	$737.32		$778.3408	$778.35	$778.35	$778.30