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	$124.45	10.167%	$137.1028	$137.10	$137.10	$137.10
Purchase #2	$137.87	4.573%	$144.1748	$144.17	$144.15	$144.20
Purchase #3	$65.28	9.665%	$71.5893	$71.59	$71.60	$71.60
Purchase #4	$70.43	9.190%	$76.9025	$76.90	$76.90	$76.90
Purchase #5	$68.40	12.712%	$77.095	$77.10	$77.10	$77.10
Purchase #6	$134.46	3.610%	$139.314	$139.31	$139.30	$139.30
Purchase #7	$41.34	4.270%	$43.1052	$43.11	$43.10	$43.10
7 purchase totals =	$642.23		$689.2836	$689.28	$689.25	$689.30