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	$95.44	13.187%	$108.0257	$108.03	$108.05	$108.00
Purchase #2	$212.56	12.328%	$238.7644	$238.76	$238.75	$238.80
Purchase #3	$111.65	10.677%	$123.5709	$123.57	$123.55	$123.60
Purchase #4	$83.90	9.327%	$91.7254	$91.73	$91.75	$91.70
Purchase #5	$112.30	6.705%	$119.8297	$119.83	$119.85	$119.80
Purchase #6	$100.47	11.638%	$112.1627	$112.16	$112.15	$112.20
Purchase #7	$194.73	13.649%	$221.3087	$221.31	$221.30	$221.30
7 purchase totals =	$911.05		$1,015.3875	$1,015.39	$1,015.40	$1,015.40