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	$152.97	6.245%	$162.523	$162.52	$162.50	$162.50
Purchase #2	$139.60	11.774%	$156.0365	$156.04	$156.05	$156.00
Purchase #3	$81.27	10.491%	$89.796	$89.80	$89.80	$89.80
Purchase #4	$149.58	10.781%	$165.7062	$165.71	$165.70	$165.70
Purchase #5	$156.27	10.251%	$172.2892	$172.29	$172.30	$172.30
Purchase #6	$59.57	8.751%	$64.783	$64.78	$64.80	$64.80
Purchase #7	$112.84	4.237%	$117.621	$117.62	$117.60	$117.60
7 purchase totals =	$852.10		$928.7549	$928.76	$928.75	$928.70