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	$150.95	11.428%	$168.2006	$168.20	$168.20	$168.20
Purchase #2	$130.48	10.816%	$144.5927	$144.59	$144.60	$144.60
Purchase #3	$172.43	6.863%	$184.2639	$184.26	$184.25	$184.30
Purchase #4	$101.76	7.376%	$109.2658	$109.27	$109.25	$109.30
Purchase #5	$79.78	12.451%	$89.7134	$89.71	$89.70	$89.70
Purchase #6	$182.64	4.661%	$191.1529	$191.15	$191.15	$191.20
Purchase #7	$171.88	13.121%	$194.4324	$194.43	$194.45	$194.40
7 purchase totals =	$989.92		$1,081.6217	$1,081.61	$1,081.60	$1,081.70