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	$16.65	8.531%	$18.0704	$18.07	$18.05	$18.10
Purchase #2	$248.40	6.403%	$264.3051	$264.31	$264.30	$264.30
Purchase #3	$167.27	9.569%	$183.2761	$183.28	$183.30	$183.30
Purchase #4	$77.85	9.741%	$85.4334	$85.43	$85.45	$85.40
Purchase #5	$141.31	9.360%	$154.5366	$154.54	$154.55	$154.50
Purchase #6	$231.61	13.711%	$263.366	$263.37	$263.35	$263.40
Purchase #7	$208.95	8.752%	$227.2373	$227.24	$227.25	$227.20
7 purchase totals =	$1,092.04		$1,196.2249	$1,196.24	$1,196.25	$1,196.20