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	$100.57	4.453%	$105.0484	$105.05	$105.05	$105.00
Purchase #2	$236.85	8.183%	$256.2314	$256.23	$256.25	$256.20
Purchase #3	$37.44	12.411%	$42.0867	$42.09	$42.10	$42.10
Purchase #4	$82.61	10.321%	$91.1362	$91.14	$91.15	$91.10
Purchase #5	$38.35	7.585%	$41.2588	$41.26	$41.25	$41.30
Purchase #6	$225.55	11.859%	$252.298	$252.30	$252.30	$252.30
Purchase #7	$150.60	11.299%	$167.6163	$167.62	$167.60	$167.60
7 purchase totals =	$871.97		$955.6758	$955.69	$955.70	$955.60