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	$120.92	8.541%	$131.2478	$131.25	$131.25	$131.20
Purchase #2	$90.60	6.589%	$96.5696	$96.57	$96.55	$96.60
Purchase #3	$160.27	13.321%	$181.6196	$181.62	$181.60	$181.60
Purchase #4	$80.71	12.322%	$90.6551	$90.66	$90.65	$90.70
Purchase #5	$69.38	6.122%	$73.6274	$73.63	$73.65	$73.60
Purchase #6	$69.67	8.571%	$75.6414	$75.64	$75.65	$75.60
Purchase #7	$118.62	10.620%	$131.2174	$131.22	$131.20	$131.20
7 purchase totals =	$710.17		$780.5783	$780.59	$780.55	$780.50