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	$127.57	5.419%	$134.483	$134.48	$134.50	$134.50
Purchase #2	$246.88	13.185%	$279.4311	$279.43	$279.45	$279.40
Purchase #3	$222.55	8.121%	$240.6233	$240.62	$240.60	$240.60
Purchase #4	$165.50	13.710%	$188.1901	$188.19	$188.20	$188.20
Purchase #5	$121.73	9.115%	$132.8257	$132.83	$132.85	$132.80
Purchase #6	$226.47	3.125%	$233.5472	$233.55	$233.55	$233.50
Purchase #7	$75.75	3.128%	$78.1195	$78.12	$78.10	$78.10
7 purchase totals =	$1,186.45		$1,287.2199	$1,287.22	$1,287.25	$1,287.10