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	$27.97	11.262%	$31.12	$31.12	$31.10	$31.10
Purchase #2	$26.65	7.760%	$28.718	$28.72	$28.70	$28.70
Purchase #3	$73.97	9.554%	$81.0371	$81.04	$81.05	$81.00
Purchase #4	$29.76	12.868%	$33.5895	$33.59	$33.60	$33.60
Purchase #5	$92.39	8.598%	$100.3337	$100.33	$100.35	$100.30
Purchase #6	$163.28	13.723%	$185.6869	$185.69	$185.70	$185.70
Purchase #7	$160.71	4.223%	$167.4968	$167.50	$167.50	$167.50
7 purchase totals =	$574.73		$627.9820	$627.99	$628.00	$627.90