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	$52.54	6.782%	$56.1033	$56.10	$56.10	$56.10
Purchase #2	$27.52	6.190%	$29.2235	$29.22	$29.20	$29.20
Purchase #3	$83.75	11.450%	$93.3394	$93.34	$93.35	$93.30
Purchase #4	$222.42	13.843%	$253.2096	$253.21	$253.20	$253.20
Purchase #5	$87.28	10.403%	$96.3597	$96.36	$96.35	$96.40
Purchase #6	$69.31	12.182%	$77.7533	$77.75	$77.75	$77.80
Purchase #7	$53.86	10.425%	$59.4749	$59.47	$59.45	$59.50
7 purchase totals =	$596.68		$665.4637	$665.45	$665.40	$665.50