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	$27.44	8.807%	$29.8566	$29.86	$29.85	$29.90
Purchase #2	$177.88	3.582%	$184.2517	$184.25	$184.25	$184.30
Purchase #3	$150.41	3.614%	$155.8458	$155.85	$155.85	$155.80
Purchase #4	$35.58	4.803%	$37.2889	$37.29	$37.30	$37.30
Purchase #5	$188.78	7.237%	$202.442	$202.44	$202.45	$202.40
Purchase #6	$45.90	5.743%	$48.536	$48.54	$48.55	$48.50
Purchase #7	$85.75	4.158%	$89.3155	$89.32	$89.30	$89.30
7 purchase totals =	$711.74		$747.5365	$747.55	$747.55	$747.50