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	$26.54	9.797%	$29.1401	$29.14	$29.15	$29.10
Purchase #2	$159.31	4.308%	$166.1731	$166.17	$166.15	$166.20
Purchase #3	$95.33	4.240%	$99.372	$99.37	$99.35	$99.40
Purchase #4	$63.71	5.577%	$67.2631	$67.26	$67.25	$67.30
Purchase #5	$96.52	6.768%	$103.0525	$103.05	$103.05	$103.10
Purchase #6	$40.74	6.153%	$43.2467	$43.25	$43.25	$43.20
Purchase #7	$147.26	9.287%	$160.936	$160.94	$160.95	$160.90
7 purchase totals =	$629.41		$669.1835	$669.18	$669.15	$669.20