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	$163.41	13.355%	$185.2334	$185.23	$185.25	$185.20
Purchase #2	$145.93	9.286%	$159.4811	$159.48	$159.50	$159.50
Purchase #3	$36.28	10.665%	$40.1493	$40.15	$40.15	$40.10
Purchase #4	$199.54	6.799%	$213.1067	$213.11	$213.10	$213.10
Purchase #5	$167.55	8.346%	$181.5337	$181.53	$181.55	$181.50
Purchase #6	$79.59	3.809%	$82.6216	$82.62	$82.60	$82.60
Purchase #7	$250.79	11.549%	$279.7537	$279.75	$279.75	$279.80
7 purchase totals =	$1,043.09		$1,141.8795	$1,141.87	$1,141.90	$1,141.80