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	$123.43	5.791%	$130.5778	$130.58	$130.60	$130.60
Purchase #2	$87.44	11.417%	$97.423	$97.42	$97.40	$97.40
Purchase #3	$45.71	8.173%	$49.4459	$49.45	$49.45	$49.40
Purchase #4	$23.97	9.784%	$26.3152	$26.32	$26.30	$26.30
Purchase #5	$99.52	5.110%	$104.6055	$104.61	$104.60	$104.60
Purchase #6	$46.57	9.473%	$50.9816	$50.98	$51.00	$51.00
Purchase #7	$66.54	9.521%	$72.8753	$72.88	$72.90	$72.90
7 purchase totals =	$493.18		$532.2243	$532.24	$532.25	$532.20