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	$173.97	9.194%	$189.9648	$189.96	$189.95	$190.00
Purchase #2	$151.68	12.564%	$170.7371	$170.74	$170.75	$170.70
Purchase #3	$78.56	8.858%	$85.5188	$85.52	$85.50	$85.50
Purchase #4	$233.92	9.348%	$255.7868	$255.79	$255.80	$255.80
Purchase #5	$56.87	13.336%	$64.4542	$64.45	$64.45	$64.50
Purchase #6	$161.60	5.843%	$171.0423	$171.04	$171.05	$171.00
Purchase #7	$213.90	5.350%	$225.3437	$225.34	$225.35	$225.30
7 purchase totals =	$1,070.50		$1,162.8477	$1,162.84	$1,162.85	$1,162.80