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	$132.27	12.469%	$148.7627	$148.76	$148.75	$148.80
Purchase #2	$154.50	6.375%	$164.3494	$164.35	$164.35	$164.30
Purchase #3	$198.88	7.169%	$213.1377	$213.14	$213.15	$213.10
Purchase #4	$97.96	3.708%	$101.5924	$101.59	$101.60	$101.60
Purchase #5	$11.56	6.772%	$12.3428	$12.34	$12.35	$12.30
Purchase #6	$104.74	13.320%	$118.6914	$118.69	$118.70	$118.70
Purchase #7	$64.73	10.752%	$71.6898	$71.69	$71.70	$71.70
7 purchase totals =	$764.64		$830.5662	$830.56	$830.60	$830.50