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	$177.94	5.673%	$188.0345	$188.03	$188.05	$188.00
Purchase #2	$169.31	12.282%	$190.1047	$190.10	$190.10	$190.10
Purchase #3	$30.51	4.249%	$31.8064	$31.81	$31.80	$31.80
Purchase #4	$102.78	12.376%	$115.5001	$115.50	$115.50	$115.50
Purchase #5	$137.61	4.841%	$144.2717	$144.27	$144.25	$144.30
Purchase #6	$143.30	11.848%	$160.2782	$160.28	$160.30	$160.30
Purchase #7	$151.59	11.731%	$169.373	$169.37	$169.35	$169.40
7 purchase totals =	$913.04		$999.3686	$999.36	$999.35	$999.40