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	$79.26	8.661%	$86.1247	$86.12	$86.10	$86.10
Purchase #2	$243.46	6.446%	$259.1534	$259.15	$259.15	$259.20
Purchase #3	$225.43	5.866%	$238.6537	$238.65	$238.65	$238.70
Purchase #4	$34.27	12.315%	$38.4904	$38.49	$38.50	$38.50
Purchase #5	$166.36	7.287%	$178.4827	$178.48	$178.50	$178.50
Purchase #6	$116.93	12.135%	$131.1195	$131.12	$131.10	$131.10
Purchase #7	$136.39	6.642%	$145.449	$145.45	$145.45	$145.40
7 purchase totals =	$1,002.10		$1,077.4734	$1,077.46	$1,077.45	$1,077.50