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	$227.75	4.111%	$237.1128	$237.11	$237.10	$237.10
Purchase #2	$142.93	9.424%	$156.3997	$156.40	$156.40	$156.40
Purchase #3	$108.46	7.744%	$116.8591	$116.86	$116.85	$116.90
Purchase #4	$133.86	8.759%	$145.5848	$145.58	$145.60	$145.60
Purchase #5	$159.62	9.176%	$174.2667	$174.27	$174.25	$174.30
Purchase #6	$188.41	9.243%	$205.8247	$205.82	$205.80	$205.80
Purchase #7	$119.49	10.317%	$131.8178	$131.82	$131.80	$131.80
7 purchase totals =	$1,080.52		$1,167.8656	$1,167.86	$1,167.80	$1,167.90