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	$52.75	13.241%	$59.7346	$59.73	$59.75	$59.70
Purchase #2	$18.36	3.594%	$19.0199	$19.02	$19.00	$19.00
Purchase #3	$16.99	11.324%	$18.9139	$18.91	$18.90	$18.90
Purchase #4	$117.51	12.718%	$132.4549	$132.45	$132.45	$132.50
Purchase #5	$138.40	9.492%	$151.5369	$151.54	$151.55	$151.50
Purchase #6	$228.41	12.424%	$256.7877	$256.79	$256.80	$256.80
Purchase #7	$182.79	7.475%	$196.4536	$196.45	$196.45	$196.50
7 purchase totals =	$755.21		$834.9015	$834.89	$834.90	$834.90