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	$207.76	13.263%	$235.3152	$235.32	$235.30	$235.30
Purchase #2	$245.91	9.786%	$269.9748	$269.97	$269.95	$270.00
Purchase #3	$81.82	10.442%	$90.3636	$90.36	$90.35	$90.40
Purchase #4	$139.39	13.659%	$158.4293	$158.43	$158.45	$158.40
Purchase #5	$244.25	7.315%	$262.1169	$262.12	$262.10	$262.10
Purchase #6	$57.43	4.292%	$59.8949	$59.89	$59.90	$59.90
Purchase #7	$17.33	9.659%	$19.0039	$19.00	$19.00	$19.00
7 purchase totals =	$993.89		$1,095.0986	$1,095.09	$1,095.05	$1,095.10