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	$200.53	11.330%	$223.25	$223.25	$223.25	$223.30
Purchase #2	$88.76	9.773%	$97.4345	$97.43	$97.45	$97.40
Purchase #3	$144.85	4.167%	$150.8859	$150.89	$150.90	$150.90
Purchase #4	$171.88	10.435%	$189.8157	$189.82	$189.80	$189.80
Purchase #5	$22.59	10.620%	$24.9891	$24.99	$25.00	$25.00
Purchase #6	$107.80	6.289%	$114.5795	$114.58	$114.60	$114.60
Purchase #7	$28.51	4.713%	$29.8537	$29.85	$29.85	$29.90
7 purchase totals =	$764.92		$830.8084	$830.81	$830.85	$830.90