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	$105.82	6.111%	$112.2867	$112.29	$112.30	$112.30
Purchase #2	$247.60	12.819%	$279.3398	$279.34	$279.35	$279.30
Purchase #3	$41.45	7.434%	$44.5314	$44.53	$44.55	$44.50
Purchase #4	$104.44	5.280%	$109.9544	$109.95	$109.95	$110.00
Purchase #5	$233.28	12.759%	$263.0442	$263.04	$263.05	$263.00
Purchase #6	$160.70	6.433%	$171.0378	$171.04	$171.05	$171.00
Purchase #7	$66.94	5.738%	$70.781	$70.78	$70.80	$70.80
7 purchase totals =	$960.23		$1,050.9753	$1,050.97	$1,051.05	$1,050.90