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	$19.27	5.334%	$20.2979	$20.30	$20.30	$20.30
Purchase #2	$30.44	10.367%	$33.5957	$33.60	$33.60	$33.60
Purchase #3	$31.94	4.195%	$33.2799	$33.28	$33.30	$33.30
Purchase #4	$170.68	10.148%	$188.0006	$188.00	$188.00	$188.00
Purchase #5	$207.54	5.334%	$218.6102	$218.61	$218.60	$218.60
Purchase #6	$219.94	10.748%	$243.5792	$243.58	$243.60	$243.60
Purchase #7	$151.84	12.289%	$170.4996	$170.50	$170.50	$170.50
7 purchase totals =	$831.65		$907.8631	$907.87	$907.90	$907.90