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	$29.85	6.463%	$31.7792	$31.78	$31.80	$31.80
Purchase #2	$74.83	13.664%	$85.0548	$85.05	$85.05	$85.10
Purchase #3	$150.66	7.680%	$162.2307	$162.23	$162.25	$162.20
Purchase #4	$173.85	8.705%	$188.9836	$188.98	$189.00	$189.00
Purchase #5	$28.84	13.745%	$32.8041	$32.80	$32.80	$32.80
Purchase #6	$151.51	8.739%	$164.7505	$164.75	$164.75	$164.80
Purchase #7	$210.69	5.565%	$222.4149	$222.41	$222.40	$222.40
7 purchase totals =	$820.23		$888.0178	$888.00	$888.05	$888.10