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	$17.90	13.348%	$20.2893	$20.29	$20.30	$20.30
Purchase #2	$90.43	11.255%	$100.6079	$100.61	$100.60	$100.60
Purchase #3	$154.33	7.506%	$165.914	$165.91	$165.90	$165.90
Purchase #4	$64.28	12.822%	$72.522	$72.52	$72.50	$72.50
Purchase #5	$126.33	10.803%	$139.9774	$139.98	$140.00	$140.00
Purchase #6	$228.54	5.496%	$241.1006	$241.10	$241.10	$241.10
Purchase #7	$181.47	5.661%	$191.743	$191.74	$191.75	$191.70
7 purchase totals =	$863.28		$932.1542	$932.15	$932.15	$932.10