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	$27.79	4.517%	$29.0453	$29.05	$29.05	$29.00
Purchase #2	$22.55	7.335%	$24.204	$24.20	$24.20	$24.20
Purchase #3	$69.32	5.132%	$72.8775	$72.88	$72.90	$72.90
Purchase #4	$79.76	11.632%	$89.0377	$89.04	$89.05	$89.00
Purchase #5	$194.45	12.840%	$219.4174	$219.42	$219.40	$219.40
Purchase #6	$144.62	4.322%	$150.8705	$150.87	$150.85	$150.90
Purchase #7	$65.74	4.597%	$68.7621	$68.76	$68.75	$68.80
7 purchase totals =	$604.23		$654.2145	$654.22	$654.20	$654.20