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	$186.51	10.550%	$206.1868	$206.19	$206.20	$206.20
Purchase #2	$71.91	9.810%	$78.9644	$78.96	$78.95	$79.00
Purchase #3	$116.41	9.242%	$127.1686	$127.17	$127.15	$127.20
Purchase #4	$203.48	9.226%	$222.2531	$222.25	$222.25	$222.30
Purchase #5	$83.43	6.317%	$88.7003	$88.70	$88.70	$88.70
Purchase #6	$112.83	12.684%	$127.1414	$127.14	$127.15	$127.10
Purchase #7	$126.98	5.838%	$134.3931	$134.39	$134.40	$134.40
7 purchase totals =	$901.55		$984.8077	$984.80	$984.80	$984.90