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	$196.37	9.789%	$215.5927	$215.59	$215.60	$215.60
Purchase #2	$184.47	6.819%	$197.049	$197.05	$197.05	$197.00
Purchase #3	$19.26	9.198%	$21.0315	$21.03	$21.05	$21.00
Purchase #4	$127.68	6.741%	$136.2869	$136.29	$136.30	$136.30
Purchase #5	$101.89	12.593%	$114.721	$114.72	$114.70	$114.70
Purchase #6	$69.56	13.109%	$78.6786	$78.68	$78.70	$78.70
Purchase #7	$78.78	11.810%	$88.0839	$88.08	$88.10	$88.10
7 purchase totals =	$778.01		$851.4436	$851.44	$851.50	$851.40