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	$172.92	7.608%	$186.0758	$186.08	$186.10	$186.10
Purchase #2	$233.67	9.192%	$255.1489	$255.15	$255.15	$255.10
Purchase #3	$37.45	12.817%	$42.25	$42.25	$42.25	$42.30
Purchase #4	$187.79	12.659%	$211.5623	$211.56	$211.55	$211.60
Purchase #5	$219.27	13.577%	$249.0403	$249.04	$249.05	$249.00
Purchase #6	$43.80	11.642%	$48.8992	$48.90	$48.90	$48.90
Purchase #7	$106.71	9.141%	$116.4644	$116.46	$116.45	$116.50
7 purchase totals =	$1,001.61		$1,109.4409	$1,109.44	$1,109.45	$1,109.50