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	$68.53	6.179%	$72.7645	$72.76	$72.75	$72.80
Purchase #2	$109.63	3.422%	$113.3815	$113.38	$113.40	$113.40
Purchase #3	$109.30	7.554%	$117.5565	$117.56	$117.55	$117.60
Purchase #4	$185.81	3.212%	$191.7782	$191.78	$191.80	$191.80
Purchase #5	$14.49	9.523%	$15.8699	$15.87	$15.85	$15.90
Purchase #6	$176.94	8.124%	$191.3146	$191.31	$191.30	$191.30
Purchase #7	$64.51	9.212%	$70.4527	$70.45	$70.45	$70.50
7 purchase totals =	$729.21		$773.1179	$773.11	$773.10	$773.30