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	$149.43	12.534%	$168.1596	$168.16	$168.15	$168.20
Purchase #2	$174.55	12.377%	$196.1541	$196.15	$196.15	$196.20
Purchase #3	$90.80	12.676%	$102.3098	$102.31	$102.30	$102.30
Purchase #4	$186.25	5.158%	$195.8568	$195.86	$195.85	$195.90
Purchase #5	$5.81	11.336%	$6.4686	$6.47	$6.45	$6.50
Purchase #6	$163.46	6.831%	$174.626	$174.63	$174.65	$174.60
Purchase #7	$20.95	9.425%	$22.9245	$22.92	$22.90	$22.90
7 purchase totals =	$791.25		$866.4994	$866.50	$866.45	$866.60