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	$80.69	13.158%	$91.3072	$91.31	$91.30	$91.30
Purchase #2	$97.73	5.115%	$102.7289	$102.73	$102.75	$102.70
Purchase #3	$250.31	4.413%	$261.3562	$261.36	$261.35	$261.40
Purchase #4	$178.27	7.396%	$191.4548	$191.45	$191.45	$191.50
Purchase #5	$99.30	6.190%	$105.4467	$105.45	$105.45	$105.40
Purchase #6	$90.39	10.155%	$99.5691	$99.57	$99.55	$99.60
Purchase #7	$222.68	8.507%	$241.6234	$241.62	$241.60	$241.60
7 purchase totals =	$1,019.37		$1,093.4863	$1,093.49	$1,093.45	$1,093.50