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	$79.69	12.713%	$89.821	$89.82	$89.80	$89.80
Purchase #2	$166.25	4.458%	$173.6614	$173.66	$173.65	$173.70
Purchase #3	$193.41	13.850%	$220.1973	$220.20	$220.20	$220.20
Purchase #4	$84.96	11.457%	$94.6939	$94.69	$94.70	$94.70
Purchase #5	$117.93	8.455%	$127.901	$127.90	$127.90	$127.90
Purchase #6	$73.96	6.613%	$78.851	$78.85	$78.85	$78.90
Purchase #7	$187.57	4.748%	$196.4758	$196.48	$196.50	$196.50
7 purchase totals =	$903.77		$981.6014	$981.60	$981.60	$981.70