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	$151.54	9.605%	$166.0954	$166.10	$166.10	$166.10
Purchase #2	$246.69	6.379%	$262.4264	$262.43	$262.45	$262.40
Purchase #3	$158.77	5.625%	$167.7008	$167.70	$167.70	$167.70
Purchase #4	$29.82	6.782%	$31.8424	$31.84	$31.85	$31.80
Purchase #5	$80.87	10.809%	$89.6112	$89.61	$89.60	$89.60
Purchase #6	$53.92	8.123%	$58.2999	$58.30	$58.30	$58.30
Purchase #7	$47.51	8.109%	$51.3626	$51.36	$51.35	$51.40
7 purchase totals =	$769.12		$827.3387	$827.34	$827.35	$827.30