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	$24.94	13.528%	$28.3139	$28.31	$28.30	$28.30
Purchase #2	$153.31	7.715%	$165.1379	$165.14	$165.15	$165.10
Purchase #3	$181.33	12.276%	$203.5901	$203.59	$203.60	$203.60
Purchase #4	$34.62	8.525%	$37.5714	$37.57	$37.55	$37.60
Purchase #5	$246.91	12.836%	$278.6034	$278.60	$278.60	$278.60
Purchase #6	$52.33	6.111%	$55.5279	$55.53	$55.55	$55.50
Purchase #7	$60.56	3.428%	$62.636	$62.64	$62.65	$62.60
7 purchase totals =	$754.00		$831.3806	$831.38	$831.40	$831.30