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	$174.45	8.391%	$189.0881	$189.09	$189.10	$189.10
Purchase #2	$94.94	9.129%	$103.6071	$103.61	$103.60	$103.60
Purchase #3	$166.25	3.128%	$171.4503	$171.45	$171.45	$171.50
Purchase #4	$34.83	7.178%	$37.3301	$37.33	$37.35	$37.30
Purchase #5	$40.61	3.279%	$41.9416	$41.94	$41.95	$41.90
Purchase #6	$115.79	4.191%	$120.6428	$120.64	$120.65	$120.60
Purchase #7	$222.72	3.143%	$229.7201	$229.72	$229.70	$229.70
7 purchase totals =	$849.59		$893.7801	$893.78	$893.80	$893.70