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	$35.77	11.314%	$39.817	$39.82	$39.80	$39.80
Purchase #2	$105.31	10.419%	$116.2822	$116.28	$116.30	$116.30
Purchase #3	$61.69	9.690%	$67.6678	$67.67	$67.65	$67.70
Purchase #4	$197.71	12.806%	$223.0287	$223.03	$223.05	$223.00
Purchase #5	$132.57	5.429%	$139.7672	$139.77	$139.75	$139.80
Purchase #6	$69.47	9.227%	$75.88	$75.88	$75.90	$75.90
Purchase #7	$28.42	10.789%	$31.4862	$31.49	$31.50	$31.50
7 purchase totals =	$630.94		$693.9291	$693.94	$693.95	$694.00