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	$40.79	5.667%	$43.1016	$43.10	$43.10	$43.10
Purchase #2	$162.41	4.306%	$169.4034	$169.40	$169.40	$169.40
Purchase #3	$37.38	7.630%	$40.2321	$40.23	$40.25	$40.20
Purchase #4	$143.52	4.627%	$150.1607	$150.16	$150.15	$150.20
Purchase #5	$149.53	6.448%	$159.1717	$159.17	$159.15	$159.20
Purchase #6	$156.26	3.758%	$162.1323	$162.13	$162.15	$162.10
Purchase #7	$81.32	10.537%	$89.8887	$89.89	$89.90	$89.90
7 purchase totals =	$771.21		$814.0905	$814.08	$814.10	$814.10