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	$19.38	6.713%	$20.681	$20.68	$20.70	$20.70
Purchase #2	$222.50	3.709%	$230.7525	$230.75	$230.75	$230.80
Purchase #3	$185.75	5.693%	$196.3247	$196.32	$196.30	$196.30
Purchase #4	$17.31	9.253%	$18.9117	$18.91	$18.90	$18.90
Purchase #5	$144.75	3.435%	$149.7222	$149.72	$149.70	$149.70
Purchase #6	$143.36	13.405%	$162.5774	$162.58	$162.60	$162.60
Purchase #7	$110.77	3.442%	$114.5827	$114.58	$114.60	$114.60
7 purchase totals =	$843.82		$893.5522	$893.54	$893.55	$893.60