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	$54.36	9.636%	$59.5981	$59.60	$59.60	$59.60
Purchase #2	$53.71	3.397%	$55.5345	$55.53	$55.55	$55.50
Purchase #3	$205.66	3.806%	$213.4874	$213.49	$213.50	$213.50
Purchase #4	$94.31	5.487%	$99.4848	$99.48	$99.50	$99.50
Purchase #5	$111.80	13.334%	$126.7074	$126.71	$126.70	$126.70
Purchase #6	$99.86	5.721%	$105.573	$105.57	$105.55	$105.60
Purchase #7	$26.95	8.419%	$29.2189	$29.22	$29.20	$29.20
7 purchase totals =	$646.65		$689.6041	$689.60	$689.60	$689.60