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	$90.99	13.799%	$103.5457	$103.55	$103.55	$103.50
Purchase #2	$39.91	9.575%	$43.7314	$43.73	$43.75	$43.70
Purchase #3	$63.85	12.370%	$71.7482	$71.75	$71.75	$71.70
Purchase #4	$23.26	9.837%	$25.5481	$25.55	$25.55	$25.50
Purchase #5	$158.71	4.642%	$166.0773	$166.08	$166.10	$166.10
Purchase #6	$92.86	11.291%	$103.3448	$103.34	$103.35	$103.30
Purchase #7	$40.68	11.440%	$45.3338	$45.33	$45.35	$45.30
7 purchase totals =	$510.26		$559.3293	$559.33	$559.40	$559.10