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	$98.59	5.592%	$104.1032	$104.10	$104.10	$104.10
Purchase #2	$227.83	13.159%	$257.8101	$257.81	$257.80	$257.80
Purchase #3	$123.88	3.225%	$127.8751	$127.88	$127.90	$127.90
Purchase #4	$60.52	13.216%	$68.5183	$68.52	$68.50	$68.50
Purchase #5	$185.59	13.758%	$211.1235	$211.12	$211.10	$211.10
Purchase #6	$56.33	5.243%	$59.2834	$59.28	$59.30	$59.30
Purchase #7	$22.26	12.711%	$25.0895	$25.09	$25.10	$25.10
7 purchase totals =	$775.00		$853.8031	$853.80	$853.80	$853.80