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	$157.83	8.800%	$171.719	$171.72	$171.70	$171.70
Purchase #2	$145.70	8.859%	$158.6076	$158.61	$158.60	$158.60
Purchase #3	$84.38	6.830%	$90.1432	$90.14	$90.15	$90.10
Purchase #4	$67.36	11.712%	$75.2492	$75.25	$75.25	$75.20
Purchase #5	$15.27	3.366%	$15.784	$15.78	$15.80	$15.80
Purchase #6	$72.36	9.143%	$78.9759	$78.98	$79.00	$79.00
Purchase #7	$65.95	10.808%	$73.0779	$73.08	$73.10	$73.10
7 purchase totals =	$608.85		$663.5568	$663.56	$663.60	$663.50