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	$59.98	12.373%	$67.4013	$67.40	$67.40	$67.40
Purchase #2	$116.37	10.581%	$128.6831	$128.68	$128.70	$128.70
Purchase #3	$103.71	9.165%	$113.215	$113.22	$113.20	$113.20
Purchase #4	$148.44	11.427%	$165.4022	$165.40	$165.40	$165.40
Purchase #5	$19.63	9.246%	$21.445	$21.45	$21.45	$21.40
Purchase #6	$133.88	4.312%	$139.6529	$139.65	$139.65	$139.70
Purchase #7	$195.32	10.295%	$215.4282	$215.43	$215.45	$215.40
7 purchase totals =	$777.33		$851.2277	$851.23	$851.25	$851.20