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	$112.65	12.262%	$126.4631	$126.46	$126.45	$126.50
Purchase #2	$19.41	11.142%	$21.5727	$21.57	$21.55	$21.60
Purchase #3	$59.46	10.830%	$65.8995	$65.90	$65.90	$65.90
Purchase #4	$166.61	13.500%	$189.1024	$189.10	$189.10	$189.10
Purchase #5	$209.57	12.211%	$235.1606	$235.16	$235.15	$235.20
Purchase #6	$72.26	11.393%	$80.4926	$80.49	$80.50	$80.50
Purchase #7	$149.29	10.850%	$165.488	$165.49	$165.50	$165.50
7 purchase totals =	$789.25		$884.1789	$884.17	$884.15	$884.30