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	$122.76	5.289%	$129.2528	$129.25	$129.25	$129.30
Purchase #2	$70.67	10.687%	$78.2225	$78.22	$78.20	$78.20
Purchase #3	$63.48	13.340%	$71.9482	$71.95	$71.95	$71.90
Purchase #4	$36.33	3.160%	$37.478	$37.48	$37.50	$37.50
Purchase #5	$43.56	5.765%	$46.0712	$46.07	$46.05	$46.10
Purchase #6	$237.59	4.347%	$247.918	$247.92	$247.90	$247.90
Purchase #7	$169.72	9.297%	$185.4989	$185.50	$185.50	$185.50
7 purchase totals =	$744.11		$796.3896	$796.39	$796.35	$796.40