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	$166.58	3.782%	$172.8801	$172.88	$172.90	$172.90
Purchase #2	$117.54	6.645%	$125.3505	$125.35	$125.35	$125.40
Purchase #3	$235.30	5.242%	$247.6344	$247.63	$247.65	$247.60
Purchase #4	$131.46	10.655%	$145.4671	$145.47	$145.45	$145.50
Purchase #5	$46.81	8.813%	$50.9354	$50.94	$50.95	$50.90
Purchase #6	$165.86	3.231%	$171.2189	$171.22	$171.20	$171.20
Purchase #7	$170.25	11.358%	$189.587	$189.59	$189.60	$189.60
7 purchase totals =	$1,033.80		$1,103.0734	$1,103.08	$1,103.10	$1,103.10