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	$243.50	4.846%	$255.3	$255.30	$255.30	$255.30
Purchase #2	$75.36	8.497%	$81.7633	$81.76	$81.75	$81.80
Purchase #3	$130.25	11.651%	$145.4254	$145.43	$145.45	$145.40
Purchase #4	$75.43	8.168%	$81.5911	$81.59	$81.60	$81.60
Purchase #5	$24.82	4.114%	$25.8411	$25.84	$25.85	$25.80
Purchase #6	$131.27	7.658%	$141.3227	$141.32	$141.30	$141.30
Purchase #7	$162.75	3.785%	$168.9101	$168.91	$168.90	$168.90
7 purchase totals =	$843.38		$900.1537	$900.15	$900.15	$900.10