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	$78.54	6.279%	$83.4715	$83.47	$83.45	$83.50
Purchase #2	$65.84	9.198%	$71.896	$71.90	$71.90	$71.90
Purchase #3	$102.89	10.432%	$113.6235	$113.62	$113.60	$113.60
Purchase #4	$70.71	5.415%	$74.5389	$74.54	$74.55	$74.50
Purchase #5	$101.53	4.845%	$106.4491	$106.45	$106.45	$106.40
Purchase #6	$216.44	11.394%	$241.1012	$241.10	$241.10	$241.10
Purchase #7	$84.88	7.821%	$91.5185	$91.52	$91.50	$91.50
7 purchase totals =	$720.83		$782.5987	$782.60	$782.55	$782.50