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	$148.76	8.571%	$161.5102	$161.51	$161.50	$161.50
Purchase #2	$79.57	12.149%	$89.237	$89.24	$89.25	$89.20
Purchase #3	$5.64	13.673%	$6.4112	$6.41	$6.40	$6.40
Purchase #4	$161.25	3.621%	$167.0889	$167.09	$167.10	$167.10
Purchase #5	$6.45	13.346%	$7.3108	$7.31	$7.30	$7.30
Purchase #6	$51.61	4.135%	$53.7441	$53.74	$53.75	$53.70
Purchase #7	$142.41	8.427%	$154.4109	$154.41	$154.40	$154.40
7 purchase totals =	$595.69		$639.7131	$639.71	$639.70	$639.60