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	$235.80	11.718%	$263.431	$263.43	$263.45	$263.40
Purchase #2	$131.89	5.809%	$139.5515	$139.55	$139.55	$139.60
Purchase #3	$127.70	4.455%	$133.389	$133.39	$133.40	$133.40
Purchase #4	$129.46	3.568%	$134.0791	$134.08	$134.10	$134.10
Purchase #5	$41.61	10.375%	$45.927	$45.93	$45.95	$45.90
Purchase #6	$43.31	12.635%	$48.7822	$48.78	$48.80	$48.80
Purchase #7	$72.82	13.677%	$82.7796	$82.78	$82.80	$82.80
7 purchase totals =	$782.59		$847.9394	$847.94	$848.05	$848.00