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	$121.52	8.532%	$131.8881	$131.89	$131.90	$131.90
Purchase #2	$250.80	11.298%	$279.1354	$279.14	$279.15	$279.10
Purchase #3	$43.26	5.419%	$45.6043	$45.60	$45.60	$45.60
Purchase #4	$68.89	5.405%	$72.6135	$72.61	$72.60	$72.60
Purchase #5	$167.29	10.187%	$184.3318	$184.33	$184.35	$184.30
Purchase #6	$171.54	6.132%	$182.0588	$182.06	$182.05	$182.10
Purchase #7	$96.74	13.488%	$109.7883	$109.79	$109.80	$109.80
7 purchase totals =	$920.04		$1,005.4202	$1,005.42	$1,005.45	$1,005.40