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	$98.59	10.712%	$109.151	$109.15	$109.15	$109.20
Purchase #2	$109.50	6.135%	$116.2178	$116.22	$116.20	$116.20
Purchase #3	$61.88	9.589%	$67.8137	$67.81	$67.80	$67.80
Purchase #4	$116.51	11.617%	$130.045	$130.05	$130.05	$130.00
Purchase #5	$6.46	7.110%	$6.9193	$6.92	$6.90	$6.90
Purchase #6	$145.74	9.454%	$159.5183	$159.52	$159.50	$159.50
Purchase #7	$46.95	9.660%	$51.4854	$51.49	$51.50	$51.50
7 purchase totals =	$585.63		$641.1505	$641.16	$641.10	$641.10