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	$63.39	4.502%	$66.2438	$66.24	$66.25	$66.20
Purchase #2	$41.40	10.368%	$45.6924	$45.69	$45.70	$45.70
Purchase #3	$82.51	8.209%	$89.2832	$89.28	$89.30	$89.30
Purchase #4	$78.65	13.352%	$89.1513	$89.15	$89.15	$89.20
Purchase #5	$90.53	4.505%	$94.6084	$94.61	$94.60	$94.60
Purchase #6	$171.80	13.377%	$194.7817	$194.78	$194.80	$194.80
Purchase #7	$68.51	12.410%	$77.0121	$77.01	$77.00	$77.00
7 purchase totals =	$596.79		$656.7729	$656.76	$656.80	$656.80