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	$55.34	4.366%	$57.7561	$57.76	$57.75	$57.80
Purchase #2	$11.72	10.270%	$12.9236	$12.92	$12.90	$12.90
Purchase #3	$107.32	10.688%	$118.7904	$118.79	$118.80	$118.80
Purchase #4	$104.73	7.648%	$112.7398	$112.74	$112.75	$112.70
Purchase #5	$115.38	9.420%	$126.2488	$126.25	$126.25	$126.20
Purchase #6	$52.75	13.540%	$59.8924	$59.89	$59.90	$59.90
Purchase #7	$43.59	12.209%	$48.9119	$48.91	$48.90	$48.90
7 purchase totals =	$490.83		$537.2630	$537.26	$537.25	$537.20