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	$168.66	10.639%	$186.6037	$186.60	$186.60	$186.60
Purchase #2	$21.38	8.364%	$23.1682	$23.17	$23.15	$23.20
Purchase #3	$123.32	3.250%	$127.3279	$127.33	$127.35	$127.30
Purchase #4	$6.49	10.322%	$7.1599	$7.16	$7.15	$7.20
Purchase #5	$236.60	12.672%	$266.582	$266.58	$266.60	$266.60
Purchase #6	$174.95	12.352%	$196.5598	$196.56	$196.55	$196.60
Purchase #7	$99.40	5.130%	$104.4992	$104.50	$104.50	$104.50
7 purchase totals =	$830.80		$911.9007	$911.90	$911.90	$912.00