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	$143.35	13.834%	$163.181	$163.18	$163.20	$163.20
Purchase #2	$138.43	5.617%	$146.2056	$146.21	$146.20	$146.20
Purchase #3	$27.47	6.682%	$29.3055	$29.31	$29.30	$29.30
Purchase #4	$189.51	11.632%	$211.5538	$211.55	$211.55	$211.60
Purchase #5	$185.89	7.663%	$200.1348	$200.13	$200.15	$200.10
Purchase #6	$223.38	11.641%	$249.3837	$249.38	$249.40	$249.40
Purchase #7	$78.81	13.253%	$89.2547	$89.25	$89.25	$89.30
7 purchase totals =	$986.84		$1,089.0191	$1,089.01	$1,089.05	$1,089.10