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	$20.87	4.588%	$21.8275	$21.83	$21.85	$21.80
Purchase #2	$165.78	4.271%	$172.8605	$172.86	$172.85	$172.90
Purchase #3	$8.97	3.468%	$9.2811	$9.28	$9.30	$9.30
Purchase #4	$106.36	9.477%	$116.4397	$116.44	$116.45	$116.40
Purchase #5	$158.39	8.591%	$171.9973	$172.00	$172.00	$172.00
Purchase #6	$84.82	5.832%	$89.7667	$89.77	$89.75	$89.80
Purchase #7	$64.47	11.541%	$71.9105	$71.91	$71.90	$71.90
7 purchase totals =	$609.66		$654.0833	$654.09	$654.10	$654.10