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	$101.57	6.333%	$108.0024	$108.00	$108.00	$108.00
Purchase #2	$96.95	8.501%	$105.1917	$105.19	$105.20	$105.20
Purchase #3	$248.70	8.351%	$269.4689	$269.47	$269.45	$269.50
Purchase #4	$170.49	8.455%	$184.9049	$184.90	$184.90	$184.90
Purchase #5	$55.82	6.790%	$59.6102	$59.61	$59.60	$59.60
Purchase #6	$177.62	4.406%	$185.4459	$185.45	$185.45	$185.40
Purchase #7	$13.56	11.836%	$15.165	$15.17	$15.15	$15.20
7 purchase totals =	$864.71		$927.7890	$927.79	$927.75	$927.80