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	$163.43	12.868%	$184.4602	$184.46	$184.45	$184.50
Purchase #2	$154.40	8.390%	$167.3542	$167.35	$167.35	$167.40
Purchase #3	$30.62	12.370%	$34.4077	$34.41	$34.40	$34.40
Purchase #4	$35.91	13.405%	$40.7237	$40.72	$40.70	$40.70
Purchase #5	$249.90	5.304%	$263.1547	$263.15	$263.15	$263.20
Purchase #6	$51.67	7.705%	$55.6512	$55.65	$55.65	$55.70
Purchase #7	$79.50	13.172%	$89.9717	$89.97	$89.95	$90.00
7 purchase totals =	$765.43		$835.7234	$835.71	$835.65	$835.90