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	$27.77	13.576%	$31.5401	$31.54	$31.55	$31.50
Purchase #2	$61.27	9.217%	$66.9173	$66.92	$66.90	$66.90
Purchase #3	$238.66	3.652%	$247.3759	$247.38	$247.40	$247.40
Purchase #4	$200.88	7.360%	$215.6648	$215.66	$215.65	$215.70
Purchase #5	$74.78	10.647%	$82.7418	$82.74	$82.75	$82.70
Purchase #6	$72.27	6.784%	$77.1728	$77.17	$77.15	$77.20
Purchase #7	$173.55	9.709%	$190.4	$190.40	$190.40	$190.40
7 purchase totals =	$849.18		$911.8127	$911.81	$911.80	$911.80