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	$42.57	7.603%	$45.8066	$45.81	$45.80	$45.80
Purchase #2	$83.76	5.146%	$88.0703	$88.07	$88.05	$88.10
Purchase #3	$172.49	5.250%	$181.5457	$181.55	$181.55	$181.50
Purchase #4	$151.44	11.307%	$168.5633	$168.56	$168.55	$168.60
Purchase #5	$101.56	6.867%	$108.5341	$108.53	$108.55	$108.50
Purchase #6	$80.82	6.107%	$85.7557	$85.76	$85.75	$85.80
Purchase #7	$36.84	4.756%	$38.5921	$38.59	$38.60	$38.60
7 purchase totals =	$669.48		$716.8678	$716.87	$716.85	$716.90