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	$21.72	13.688%	$24.693	$24.69	$24.70	$24.70
Purchase #2	$149.34	11.350%	$166.2901	$166.29	$166.30	$166.30
Purchase #3	$187.64	3.633%	$194.457	$194.46	$194.45	$194.50
Purchase #4	$91.94	7.110%	$98.4769	$98.48	$98.50	$98.50
Purchase #5	$43.51	5.660%	$45.9727	$45.97	$45.95	$46.00
Purchase #6	$60.59	11.185%	$67.367	$67.37	$67.35	$67.40
Purchase #7	$48.27	8.774%	$52.5052	$52.51	$52.50	$52.50
7 purchase totals =	$603.01		$649.7619	$649.77	$649.75	$649.90